Display device

ABSTRACT

In view of the problem that a reduced thickness of an EL film causes a short circuit between an anode and a cathode and malfunction of a transistor, the invention provides a display device that has a light emitting element including an electrode and an electroluminescent layer, a wire electrically connected to the electrode of the light emitting element, a transistor provided with an active layer including a source, a drain and a channel forming region, and a power supply line electrically connected to one of the source and the drain of the transistor, wherein the wire is electrically connected to the other of the source and the drain of the transistor, and the width of a part of the electrode in the vicinity of a portion where the electrode is electrically connected to the wire is smaller than that of the electrode in the other portion.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method for correcting defectivepixels in a display device having a self-light emitting element. Inparticular, the invention relates to a method for correcting defectivepixels in an active matrix display device having an EL(Electroluminescence) element. The invention also relates to a displaydevice having a structure capable of easily correcting defective pixels.

2. Description of the Related Art

In recent years, a light emitting device having a light emitting elementtypified by an EL element has been actively developed, and it isexpected to be widely used by taking advantages of the self-luminoustype such as high image quality, wide viewing angle, thin thickness, andlightweight. As a light emitting element used for such a self-lightemitting display device, an organic light emitting diode (OLED) (alsocalled an organic EL element), an electroluminescence (EL) element, andthe like have been drawing attention and used for an EL display and thelike. Since the light emitting element such as an OLED is aself-luminous type, it has advantages such as higher visibility ofpixels than that in a liquid crystal display, and fast response withoutrequiring a backlight. The luminance of a light emitting element iscontrolled by a current value flowing through the light emittingelement.

An EL element has an electroluminescent layer (layer containing anorganic compound) between a cathode and an anode. The electroluminescentlayer (layer containing an organic compound) may be formed of a singlelayer (only a light emitting layer) or a plurality of stacked layers. Ifthe electroluminescent layer is formed of a plurality of layers, thelayers may be stacked in any of the following orders from asemiconductor element side (pixel electrode side): (1) an anode, a holeinjection layer, a hole transporting layer, a light emitting layer, anelectron transporting layer, and a cathode; (2) an anode, a holeinjection layer, a light emitting layer, an electron transporting layer,and a cathode; (3) an anode, a hole injection layer, a hole transportinglayer, a light emitting layer, an electron transporting layer, anelectron injection layer, and a cathode; (4) an anode, a hole injectionlayer, a hole transporting layer, a light emitting layer, a holeblocking layer, an electron transporting layer, and a cathode; (5) ananode, a hole injection layer, a hole transporting layer, a lightemitting layer, a hole blocking layer, an electron transporting layer,an electron injection layer, and a cathode. Such a structure is called aforward staggered structure, and a pixel electrode functions as ananode. On the other hand, a structure where a cathode is formed first onthe semiconductor element side (pixel electrode side) is called aninversely staggered structure, and a pixel electrode functions as acathode.

An electroluminescent layer is required to emit light and flow current.Current flowing through an electroluminescent layer decreases inverselyproportional to the power 3 of the film thickness; therefore, it isnecessary to considerably reduce the thickness of the electroluminescentlayer.

When the thickness of an electroluminescent layer is considerablyreduced, however, the following problems occur: a short circuit betweenan anode and a cathode (hereinafter referred to as a short circuitbetween two electrodes) easily occurs. This is caused by the thinthickness of the electroluminescent layer, unevenness of multilayer ofan electrode, or fine dust. In addition, due to malfunction of atransistor connected to an EL element, charges are applied in some casesto the EL element during a period when no charge is to be applied,thereby the EL element may emit light. On the contrary, due tomalfunction of a transistor connected to an EL element, charges cannotbe applied to the EL element in some cases, thereby the EL element wouldemit no light all the time. Thus, in some cases, an excess current mayflow to an electroluminescent layer of an EL element or an EL elementmay emit light during a period when no light is to be emitted, whichresults in a significant degradation in quality of a display device.Note that in this specification, among a plurality of pixels each havinga light emitting element, a pixel where a light emitting element alwaysemits light or no light or a light emitting element cannot be controlledproperly due to a short circuit between two electrodes of the lightemitting element, a short circuit between wires, a short circuit betweenan electrode of the light emitting element and a wire, or malfunction ofa transistor connected to the light emitting element, is referred to asa defective pixel.

When a defective pixel is included, a short circuit causes a voltagedrop, and it is thus difficult in some cases to apply a sufficientpotential to other pixels from a power supply line connected to eachpixel. That is to say, a light emitting element that always emits lightadversely affects light emitting elements in other pixels as well as thedefective pixel.

The case here considered is a liquid crystal display device that hasbeen growing in the display device market in recent years. In the caseof a liquid crystal display device, a liquid crystal element operates asa capacitor and holds an applied voltage, and liquid crystal moleculesare controlled by an electric field generated by the applied voltage. Inother words, current does not keep flowing to a liquid crystal element.Accordingly, even if a pixel electrode of a pixel is short circuited toanother wire, other pixels are not adversely affected as current doesnot keep flowing.

In addition, in the case of a liquid crystal element, power consumptionis not increased since current does not keep flowing. Further, ingeneral, only one transistor is provided in each pixel; therefore, onetransistor and one pixel electrode are only required to be corrected.

On the other hand, an EL element is a current-driven device, wherecurrent keeps flowing from a power supply line during a light emittingperiod. When a defect occurs in a pixel provided with an EL elementhaving such properties, other normal pixels may be adversely affectedand power consumption may be increased. In addition, at least twotransistors are provided in a pixel, and a circuit including a portionfor holding a signal, a portion for controlling the amount of currentand the like has a complex configuration. Thus, it is difficult todetermine which portion is corrected and how the portion is corrected.

Such problems do not occur in a liquid crystal display device and areunique to an electroluminescence display device where a power supplyline is required and current keeps flowing.

It is a primary object of the invention to provide a display device withimproved image quality by correcting a defective pixel, in particulardefects in a pixel where a light emitting element always emits light ora light emitting element cannot be controlled properly due to a shortcircuit between two electrodes of the light emitting element, a shortcircuit between wires, a short circuit between an electrode of the lightemitting element and a wire, or malfunction of a transistor connected tothe light emitting element. It is another object of the invention toprovide a display device having a structure capable of easily correctingdefective pixels.

SUMMARY OF THE INVENTION

In a defective pixel, particularly in a pixel having a light emittingelement that is not controlled properly and that always emits light, apotential is not applied to one electrode of the light emitting elementall the time. For example, one electrode of the light emitting elementis brought into a floating state.

According to a structure of the invention disclosed in thisspecification, at least a part of a wire between one electrode of alight emitting element and a wire (power supply line) for applying apotential to the one electrode of the light emitting element is cut off.That is to say, connection of a wire is physically cut off so that nocurrent flows therethrough.

According to the aforementioned structure of the invention, the wire iscut off by laser irradiation. As a result, the current path from a powersupply line to the light emitting element can be interrupted, therebypreventing the light emitting element from emitting light (preventingbright spots).

According to another structure of the invention disclosed in thisspecification, a transistor that is provided between a light emittingelement and a power supply line for applying a potential to the lightemitting element and connected to the light emitting element is keptoff. For example, in a normally-off transistor (enhancement transistor),a gate and a source have the same potential. That is to say, electricalconnection of a wire is interrupted so that no current flows to an ELelement during a display period.

According to another structure of the invention disclosed in thisspecification, a part of a wire between a light emitting element and apower supply line for applying a potential to the light emitting elementhas a reduced width. Note that in this specification, “the width of awire” means a distance in a direction perpendicular to the direction ofcurrent flowing through the wire. Similarly, in this specification, “thewidth of a power supply line” or “the width of an electrode” means adistance in a direction perpendicular to the direction of currentflowing through the power supply line (or the electrode).

According to the aforementioned structure of the invention, the width ofthe part of the wire is reduced to 3 μm or less.

Another structure of the invention disclosed in this specificationprovides a method for correcting defects in a display device that has aplurality of pixels each including a light emitting element providedwith an electrode and an electroluminescent layer and where at least oneor more of the plurality of pixels are defective, wherein a wireconnected to the electrode of the light emitting element provided in thedefective pixel is cut off.

Another structure of the invention disclosed in the invention provides amethod for correcting defects in a display device that has a pluralityof pixels each including a transistor and a light emitting elementprovided with an electrode and an electroluminescent layer and where atleast one or more of the plurality of pixels are defective, wherein oneof a source and a drain of the transistor is connected to the electrodeof the light emitting element through a wire, and the wire connected tothe electrode of the light emitting element provided in the defectivepixel is cut off.

Another structure of the invention disclosed in the invention provides amethod for correcting defects in a display device that has a pluralityof pixels each including a transistor and a light emitting elementprovided with an electrode and an electroluminescent layer and where atleast one or more of the plurality of pixels are defective, wherein thetransistor provided in the defective pixel is always off.

Another structure of the invention disclosed in this specificationprovides a method for correcting defects in a display device that has aplurality of pixels each including a P-channel transistor and a lightemitting element provided with an electrode and an electroluminescentlayer and where at least one or more of the plurality of pixels aredefective, wherein one of a source and a drain of the transistor isconnected to a power supply line, the other is connected to theelectrode of the light emitting element through a wire, and a gatethereof is connected to a wire having a higher potential than the powersupply line.

According to the aforementioned structure of the invention, the wireconnected to the electrode of the light emitting element provided in thedefective pixel is cut off by laser irradiation. In addition, accordingto the aforementioned structure of the invention, the light emittingelement is driven by the transistor.

Another structure of the invention disclosed in this specificationprovides a display device that has a light emitting element including anelectrode and an electroluminescent layer, a wire electrically connectedto an electrode of the light emitting element, a transistor including anactive layer provided with a source, a drain and a channel formingregion, and a power supply line electrically connected to one of thesource and the drain of the transistor, wherein the wire is electricallyconnected to the other of the source and the drain of the transistor,and the width of a part of the electrode in the vicinity of a portionwhere the electrode is electrically connected to the wire is smallerthan that of the electrode in the other portion.

According to the aforementioned structure of the invention, the width ofthe part of the electrode is reduced to 3 μm or less. Further, the widthof the part of the electrode is reduced to half or less than that of theelectrode in the other portion. In addition, the width of the part ofthe electrode is smaller than the smallest width of wires used for asignal line driver circuit and a scan line driver circuit.

Another structure of the invention disclosed in this specificationprovides a display device that has a light emitting element including anelectrode and an electroluminescent layer, a wire electrically connectedto an electrode of the light emitting element, a transistor including anactive layer provided with a source, a drain and a channel formingregion, and a power supply line electrically connected to one of thesource and the drain of the transistor, wherein the wire is electricallyconnected to the other of the source and the drain of the transistor,and the width of at least a part of the wire between a portion where theelectrode is electrically connected to the wire and a portion where thewire is electrically connected to the other of the source and the drainof the transistor is smaller than that of the wire in the other portion.

According to the aforementioned structure of the invention, the width ofthe part of the wire is reduced to 3 μm or less. Further, the width ofthe part of the wire is reduced to half or less than that of the wire inthe other portion. In addition, the width of the part of the wire issmaller than the smallest width of wires used for a signal line drivercircuit and a scan line driver circuit.

Another structure of the invention disclosed in this specificationprovides a display device that has a light emitting element including anelectrode and an electroluminescent layer, a wire electrically connectedto an electrode of the light emitting element, a transistor including anactive layer provided with a source, a drain and a channel formingregion, and a power supply line electrically connected to one of thesource and the drain of the transistor, wherein the wire is electricallyconnected to the other of the source and the drain of the transistor,and the width of a part of the power supply line in the vicinity of aportion where the power supply line is electrically connected to the oneof the source and the drain of the transistor is smaller than that ofthe power supply line in the other portion.

According to the aforementioned structure of the invention, the width ofthe part of the power supply line is reduced to 3 μm or less. Further,the width of the part of the power supply line is reduced to half orless than that of the power supply line in the other portion. Inaddition, the width of the part of the power supply line is smaller thanthe smallest width of wires used for a signal line driver circuit and ascan line driver circuit.

Another structure of the invention disclosed in this specificationprovides a display device that has a light emitting element including anelectrode and an electroluminescent layer, a wire electrically connectedto an electrode of the light emitting element, a transistor including anactive layer provided with a source, a drain and a channel formingregion, a power supply line electrically connected to one of the sourceand the drain of the transistor, and a gate wire, wherein the wire iselectrically connected to the other of the source and the drain of thetransistor, the active layer partially overlaps the wire, the gate wireand the power supply line, and the width of a part of the active layerin a portion where the active layer does not overlap the wire, the gatewire and the power supply line is smaller than that of the active layerin the other portion.

According to the aforementioned structure of the invention, the width ofthe part of the active layer is reduced to 3 μm or less. Further, thewidth of the part of the active layer is reduced to half or less thanthat of the active layer in the other portion. In addition, the width ofthe part of the active layer is smaller than the smallest width of wiresused for a signal line driver circuit and a scan line driver circuit.

According to the aforementioned structure of the invention, the activelayer of the transistor is an amorphous semiconductor film or acrystalline semiconductor film. In addition, the transistor is a topgate transistor or a bottom gate transistor.

In this specification, the light emitting element may be any of anorganic EL element, an inorganic EL element, and an element containing amixture of an organic EL and an inorganic EL. Further, it is alsopossible to adopt a display medium such as an electron emitting element,where a contrast is changed by an electrical or magnetic effect. Adisplay device using an electron emitting element includes a fieldemission display (FED), a surface-conduction electron-emitter display(SED), and the like.

In this specification, “connection” includes electrical connection.Accordingly, other elements, switches and the like may be disposedtherebetween.

In the invention, the type of applicable transistor is not especiallylimited, and a thin film transistor (hereinafter referred to as a TFT)using a non-single crystalline semiconductor film typified by amorphoussilicon and polycrystalline silicon, a MOS transistor using asemiconductor substrate or an SOI substrate, a junction transistor, abipolar transistor, a transistor using an organic semiconductor or acarbon nanotube, and other transistors may be employed. Further, thetype of substrate on which a transistor is disposed is not especiallylimited, and the transistor may be formed on a single crystallinesubstrate, an SOI substrate, a glass substrate, a plastic substrate orthe like.

In this specification, “switches” may be electrical ones or mechanicalones as long as they can control current flow. The switches may be, forexample, transistors, diodes, or logic circuits made of a combinationthereof. If a transistor is used as a switch, the polarity (conductivitytype) of the transistor is not particularly limited since it operatesonly as a switch. However, when an off-current is desirably small, it isdesirable to use a transistor having a polarity with a smalloff-current. For example, a transistor having an LDD region, amulti-gate structure or the like has a small off-current. Further, whenthe potential of a source terminal of a transistor functioning as aswitch is close to that of a low potential side power supply (Vss, Vgnd,0 V and the like), an N-channel transistor is desirably used. On theother hand, when the potential of a source terminal of a transistorfunctioning as a switch is close to that of a high potential side powersupply (Vdd and the like), a P-channel transistor is desirably used.This allows the transistor to operate efficiently as a switch becausethe absolute value of a gate-source voltage can be increased. Inaddition, a CMOS switch may be formed using both an N-channel transistorand a P-channel transistor.

As set forth above, any type of transistor may be used in the inventionand a transistor may be formed over any type of substrate. Accordingly,all the circuits for driving a pixel may be formed over a glasssubstrate, a plastic substrate, a single crystalline substrate, an SOIsubstrate, or other substrates. Alternatively, a part of the circuitsfor driving a pixel may be formed over a first substrate, and the otherpart of the circuits may be formed over a second substrate that isdifferent from the first substrate. In other words, not all the circuitsfor driving a pixel are required to be formed over the same substrate.For example, a pixel array and a gate line driver circuit may be formedover a glass substrate using TFTs, and a signal line driver circuit (ora part of it) may be formed over a single crystalline substrate.Further, the signal line driver circuit (IC chip) formed over a singlecrystalline substrate may be connected onto the glass substrate by COG(Chip On Glass), or the IC chip may be connected to the glass substrateby TAB (Tape Auto Bonding) or using a printed board.

In this specification, “a semiconductor device” means a device having asemiconductor element such as a transistor and a diode. A display devicemeans a device having a display element such as a liquid crystal elementand an EL element. A liquid crystal display device means a displaydevice having a liquid crystal element. A light emitting device means adevice having a light emitting element such as an EL element.

The invention may be applied to a display device adopting either apassive matrix driving method or an active matrix driving method.

According to the invention, defective pixels can be corrected properlyonly by adding a simple process, and it is possible to provide a displaydevice with high display quality, where no bright spots are included anddegradation in image quality of the entire screen is reduced. At thesame time, the production yield of the display device can be increased,which results in significant reduction in cost.

When the invention is applied to a pixel where the light emittingelement always emits light, among a plurality of pixels each including alight emitting element, the pixel displays black all the time.Accordingly, for example, a point defect cannot be corrected even whenthe invention is applied. However, a defective pixel is less visiblewhen a pixel emits no light during a period when light emitting elementsin all pixels are to emit light as compared to when a pixel emits lightduring a period when light emitting elements in all pixels are to emitno light. Thus, the invention can provide a display device with superiordisplay quality and significantly reduced power consumption. Inaddition, a defective pixel does not adversely affect a pixel having alight emitting element that operates normally.

In a display device having the aforementioned structures, defectivepixels can be easily corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing Embodiment Mode 1 of the invention.

FIG. 2 is a diagram showing Embodiment Mode 3 of the invention.

FIG. 3 is a diagram showing Embodiment Mode 3 of the invention.

FIG. 4 is a diagram showing Embodiment Mode 5 of the invention.

FIGS. 5A and 5B are diagrams each showing Embodiment Mode 6 of theinvention.

FIG. 6 is a diagram showing Embodiment Mode 7 of the invention.

FIG. 7 is a diagram showing Embodiment Mode 8 of the invention.

FIGS. 8A to 8F are diagrams each showing Embodiment 2 of the invention.

FIGS. 9A and 9B are diagrams each showing Embodiment Mode 6 of theinvention.

FIG. 10 is a diagram showing Embodiment 2 of the invention.

FIG. 11 is a diagram showing Embodiment Modes 1 and 4 of the invention.

FIG. 12 is a diagram showing Embodiment Modes 1 and 4 of the invention.

FIG. 13 is a diagram showing Embodiment Modes 1 and 4 of the invention.

FIG. 14 is a diagram showing Embodiment Modes 1 and 4 of the invention.

FIG. 15 is a diagram showing Embodiment Modes 1 and 4 of the invention.

FIGS. 16A and 16B are diagrams each showing Embodiment Mode 5 of theinvention.

FIG. 17 is a diagram showing Embodiment Mode 5 of the invention.

FIG. 18 is a diagram showing Embodiment Mode 9 of the invention.

FIGS. 19A and 19B are diagrams each showing Embodiment Mode 6 of theinvention.

FIGS. 20A and 20B are diagrams each showing Embodiment Mode 6 of theinvention.

FIG. 21 is a diagram showing Embodiment 1 of the invention.

FIG. 22 is a diagram showing Embodiment 1 of the invention.

FIG. 23 is a diagram showing Embodiment 1 of the invention.

FIG. 24 is a diagram showing Embodiment 1 of the invention.

FIG. 25 is a diagram showing Embodiment 1 of the invention.

FIG. 26 is a diagram showing Embodiment 1 of the invention.

FIGS. 27A and 27B are diagrams each showing Embodiment 1 of theinvention.

FIG. 28 is a diagram showing Embodiment 1 of the invention.

FIG. 29 is a diagram showing Embodiment 1 of the invention.

FIG. 30 is a diagram showing Embodiment 1 of the invention.

FIG. 31 is a diagram showing Embodiment 1 of the invention.

FIG. 32 is a diagram showing Embodiment 1 of the invention.

FIG. 33 is a diagram showing Embodiment 1 of the invention.

FIG. 34 is a diagram showing Embodiment 1 of the invention.

FIG. 35 is diagram showing Embodiment Mode 9 of the invention.

FIGS. 36A and 36B are diagrams each showing Embodiment Mode 10 of theinvention.

FIGS. 37A and 37B are diagrams each showing Embodiment Mode 11 of theinvention.

FIG. 38 is a diagram showing Embodiment Mode 12 of the invention.

FIG. 39 is a diagram showing Embodiment Mode 13 of the invention.

FIG. 40 is a diagram showing Embodiment Mode 14 of the invention.

FIG. 41 is a diagram showing Embodiment Mode 15 of the invention.

FIGS. 42A and 42B are diagrams each showing Embodiment Mode 16 of theinvention.

FIGS. 43A and 43B are diagrams each showing Embodiment Mode 17 of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention will be described by way of Embodiment Modes andEmbodiments with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the invention, they should beconstrued as being included therein. Note that in all the drawings forillustrating the invention, the identical portions or portions havingthe identical function are denoted by the identical reference numerals,and description thereof is omitted.

Embodiment Mode 1

In this embodiment mode, a method for cutting off at least a part of awire between one electrode of a light emitting element and a powersupply line for applying a potential to the one electrode of the lightemitting element is described with reference to drawings.

Description is made with reference to FIG. 11. Each pixel has a lightemitting element 101 and a transistor 1103. One of a source and a drainof the transistor 1103 is connected to a power supply line 105, and theother is connected to one electrode of the light emitting element 101.

A method for correcting defective pixels is described. If the powersupply line 105 is connected to one electrode of the light emittingelement 101 through the transistor 1103, a wire is cut off between thepower supply line 105 and one of the source and the drain of thetransistor 1103, or between the other of the source and the drain andone electrode of the light emitting element 101. For example, a portion1101 or a portion 1102 shown as an ellipse in FIG. 11 is cut off. Notethat although one portion is only required to be cut off, two or moreportions may be cut off to increase reliability.

In this manner, in the case of a short circuit between two electrodes ofthe light emitting element, a short circuit between wires, a shortcircuit between an electrode of the light emitting element and a wire,or malfunction of the transistor connected to the light emittingelement, the current path from the power supply line 105 to the otherelectrode 108 of the light emitting element 101 through the transistor1103 and the light emitting element 101 can be interrupted by cuttingoff the portion 1101 or the portion 1102. As a result, the lightemitting element 101 can be prevented from emitting light (bright spotscan be prevented).

Although the transistor 1103 in FIG. 11 is a P-channel transistor, theinvention is not limited to this. Even when the transistor 1103 is anN-channel transistor, the current path from the power supply line 105 tothe other electrode 108 of the light emitting element 101 through thetransistor 1103 and the light emitting element 101 can be interrupted bycutting off the portion 1101 or the portion 1102. Thus, the lightemitting element 101 can be prevented from emitting light (bright spotscan be prevented). Further, FIG. 11 shows a structure where thetransistor 1103 is provided between the power supply line 105 and thelight emitting element 101; however, another element may be providedinstead of the transistor 1103. In addition, the invention can beimplemented even when another element is provided between the powersupply line 105 and the light emitting element 101 in addition to thetransistor 1103.

Next, description is made with reference to FIG. 12. Each pixel has thelight emitting element 101, a first transistor 1204 and a secondtransistor 1205. One of a source and a drain of the second transistor1205 is connected to the power supply line 105 and the other isconnected to one of a source and a drain of the first transistor 1204.The other of the source and the drain of the first transistor 1204 isconnected to one electrode of the light emitting element 101. In otherwords, the power supply line 105 is connected to one electrode of thelight emitting element 101 through the first transistor 1204 and thesecond transistor 1205 that are connected in series to each other.

A method for correcting defective pixels is described. A wire is cut offbetween the power supply line 105 and one of the source and the drain ofthe second transistor 1205, between the other of the source and thedrain of the second transistor 1205 and one of the source and the drainof the first transistor 1204, or between the other of the source and thedrain of the first transistor 1204 and one electrode of the lightemitting element 101. For example, a portion 1201, a portion 1202, or aportion 1203 shown as an ellipse in FIG. 12 is cut off. Note thatalthough one portion is only required to be cut off, two or moreportions may be cut off to increase reliability.

In this manner, in the case of a short circuit between two electrodes ofthe light emitting element, a short circuit between wires, a shortcircuit between an electrode of the light emitting element and a wire,or malfunction of the transistor connected to the light emittingelement, the current path from the power supply line 105 to the otherelectrode 108 of the light emitting element 101 through the secondtransistor 1205, the first transistor 1204 and the light emittingelement 101 can be interrupted by cutting off the portion 1201, theportion 1202 or the portion 1203. As a result, the light emittingelement 101 can be prevented from emitting light (bright spots can beprevented).

Although each of the first transistor 1204 and the second transistor1205 in FIG. 12 is a P-channel transistor, the invention is not limitedto this. Even when one or both of the first transistor 1204 and thesecond transistor 1205 are N-channel transistors, the current path fromthe power supply line 105 to the other electrode 108 of the lightemitting element 101 through the second transistor 1205, the firsttransistor 1204 and the light emitting element 101 can be interrupted bycutting off the portion 1201, the portion 1202 or the portion 1203.Thus, the light emitting element 101 can be prevented from emittinglight (bright spots can be prevented). That is to say, both of the firsttransistor 1204 and the second transistor 1205 may be P-channeltransistors or N-channel transistors, or one of the two transistors maybe a P-channel transistor while the other may be an N-channeltransistor. Note that the two transistors are connected in series toeach other in FIG. 12; however, the invention is not limited to this.Three or more transistors may be connected. In that case also, a wiremay be cut off similarly to FIG. 12. Further, the invention can beimplemented even when another element is provided between the powersupply line 105 and the light emitting element 101 in addition to thefirst transistor 1204 and the second transistor 1205.

Next, description is made with reference to FIG. 13. Each pixel has thelight emitting element 101, a first transistor 1304 and a secondtransistor 1305. One of a source and a drain of the first transistor1304 is connected to a wire 1351 and the other is connected to oneelectrode of the light emitting element 101. One of a source and a drainof the second transistor 1305 is connected to a wire 1352 and the otheris connected to the one electrode of the light emitting element 101.Note that the wire 1351 and the wire 1352 may be connected to the samepower supply or different power supplies.

A method for correcting defective pixels is described. A wire is cut offboth between the wire 1351 and one of the source and the drain of thefirst transistor 1304 and between the wire 1352 and one of the sourceand the drain of the second transistor 1305. Alternatively, a wire iscut off between one electrode of the light emitting element 101 and aconnecting portion between the other of the source and the drain of thefirst transistor 1304 and the other of the source and the drain of thesecond transistor 1305. For example, a portion 1301 shown as an ellipsein FIG. 13 is cut off, or one of portions 1302 and 1311 and one ofportions 1303 and 1312 each shown as an ellipse in FIG. 13 are both cutoff.

In this manner, in the case of a short circuit between the twoelectrodes of the light emitting element, a short circuit between wires,a short circuit between an electrode of the light emitting element and awire, or malfunction of the transistor connected to the light emittingelement, the current path from the wire 1351 and the wire 1352 to theother electrode 108 of the light emitting element 101 through eachtransistor and the light emitting element 101 can be interrupted bycutting off the portion 1301, or both of the portion 1302 and theportion 1303. As a result, the light emitting element 101 can beprevented from emitting light (bright spots can be prevented).

Although each of the first transistor 1304 and the second transistor1305 in FIG. 13 is a P-channel transistor, the invention is not limitedto this. Even when each of the first transistor 1304 and the secondtransistor 1305 is an N-channel transistor, the current path from thepower supply line 105 to the other electrode 108 of the light emittingelement 101 through each transistor and the light emitting element 101can be interrupted by cutting off the portion 1301, or both of theportion 1302 and the portion 1303. Thus, the light emitting element 101can be prevented from emitting light (bright spots can be prevented).That is to say, both of the first transistor 1304 and the secondtransistor 1305 may be P-channel transistors or N-channel transistors,or one of the two transistors may be a P-channel transistor while theother may be an N-channel transistor. Note that the two transistors areconnected in parallel to each other in FIG. 13; however, the inventionis not limited to this. Three or more transistors may be connected inparallel. In that case also, a wire may be cut off similarly to FIG. 13.

The wire 1351 and the wire 1352 may be connected to any element, forexample, a power supply line, a circuit, a transistor, or a capacitor.Further, the wire 1351 and the wire 1352 may be connected to differentelements or the same element. Instead, the wire 1351 and the wire 1352may be an identical wire functioning as a power supply line.

The first transistor 1304 is not limited to one. For example, as shownin FIG. 15, another element such as a transistor may be connected inseries to the first transistor 1304. Similarly, another element such asa transistor may be connected in series to the second transistor 1305.

Description is made with reference to FIG. 15. Each pixel has the lightemitting element 101, a first transistor 1506, a second transistor 1507,and a third transistor 1508. One of a source and a drain of the secondtransistor 1507 is connected to a wire 1551, and the other is connectedto one of a source and a drain of the first transistor 1506. One of asource and a drain of a third transistor 1508 is connected to a wire1552, and the other is connected to one electrode of the light emittingelement 101. The other of the source and the drain of the firsttransistor 1506 is connected to one electrode of the light emittingelement 101. Note that the wire 1551 and the wire 1552 may be connectedto the same power supply or different power supplies.

A method for correcting defective pixels is described. The current pathfrom the wire 1551 to the other electrode 108 of the light emittingelement 101 can be interrupted by cutting off at least one of a wirebetween a connecting portion between the wire 1551 and one of the sourceand the drain of the second transistor 1507 and the one of the sourceand the drain of the second transistor 1507, a wire between the other ofthe source and the drain of the second transistor 1507 and one of thesource and the drain of the first transistor 1506, and a wire between aconnecting portion between the other of the source and the drain of thefirst transistor 1506 and one electrode of the light emitting element101 and the other of the source and the drain of the first transistor1506. Further, the current path from the wire 1552 to the otherelectrode 108 of the light emitting element 101 can be interrupted bycutting off at least one of a wire between a connecting portion betweenthe wire 1552 and one of the source and the drain of the thirdtransistor 1508 and the one of the source and the drain of the thirdtransistor 1508, and a wire between a connecting portion between theother of the source and the drain of the third transistor 1508 and oneelectrode of the light emitting element 101 and the other of the sourceand the drain of the third transistor 1508. For example, between thewires 1551 and 1552 and the one electrode of the light emitting element101, a portion 1501 or a portion 1512 shown as an ellipse in FIG. 15 iscut off, or one of portions 1502, 1504 and 1511 and one of portions 1503and 1505 each shown as an ellipse in FIG. 15 are both cut off.

In this manner, in the case of a short circuit between the twoelectrodes of the light emitting element, a short circuit between wires,a short circuit between an electrode of the light emitting element and awire, or malfunction of the transistor connected to the light emittingelement, the current path from the wire 1551 and the wire 1552 to theother electrode 108 of the light emitting element 101 through eachtransistor and the light emitting element 101 can be interrupted bycutting off the portion 1501, or both one of the portions 1502 and 1504and one of the portions 1503 and 1505. As a result, the light emittingelement 101 can be prevented from emitting light (bright spots can beprevented).

Although each of the first to third transistors 1506 to 1508 in FIG. 15is a P-channel transistor, the invention is not limited to this. That isto say, regardless of the conductivity of the first to third transistors1506 to 1508, the current path from the wire 1551 and the wire 1552 tothe other electrode 108 of the light emitting element 101 through eachtransistor and the light emitting element 101 can be interrupted bycutting off the portion 1501, or both one of the portions 1502 and 1504and one of the portions 1503 and 1505. As a result, the light emittingelement 101 can be prevented from emitting light (bright spots can beprevented).

Next, description is made with reference to FIG. 14. Each pixel has thelight emitting element 101, a first transistor 1405, a second transistor1406, and a third transistor 1407. One of a source and a drain of thesecond transistor 1406 is connected to a wire 1451, and the other isconnected to one of a source and a drain of the first transistor 1405.One of a source and a drain of the third transistor 1407 is connected toa wire 1452, and the other is connected to one of the source and thedrain of the first transistor 1405. The other of the source and thedrain of the first transistor 1405 is connected to one electrode of thelight emitting element 101. Note that the wire 1451 and the wire 1452may be connected to the same power supply or different power supplies.Further, the wire 1451 and the wire 1452 may be an identical wirefunctioning as a power supply line.

A method for correcting defective pixels is described. A wire is cut offbetween one electrode of the light emitting element 101 and the other ofthe source and the drain of the first transistor 1405. Alternatively, awire is cut off between one of the source and the drain of the firsttransistor 1405 and a connecting portion between the other of the sourceand the drain of the second transistor 1406 and the other of the sourceand the drain of the third transistor 1407. Further alternatively, awire is cut off both between one of the source and the drain of thesecond transistor 1406 and the wire 1451 and between one of the sourceand the drain of the third transistor 1407 and the wire 1452. Forexample, between the wires 1451 and 1452 and one electrode of the lightemitting element 101, a portion 1401, 1402 or 1411 shown as an ellipsein FIG. 14 is cut off, or one of portions 1403 and 1412 and one ofportions 1404 and 1413 each shown as an ellipse in FIG. 14 are both cutoff.

In this manner, in the case of a short circuit between the twoelectrodes of the light emitting element, a short circuit between wires,a short circuit between an electrode of the light emitting element and awire, or malfunction of the transistor connected to the light emittingelement, the current path from the wire 1451 and the wire 1452 to theother electrode 108 of the light emitting element 101 through eachtransistor and the light emitting element 101 can be interrupted bycutting off the portion 1401 or 1402, or both of the portion 1403 andthe portion 1404. As a result, the light emitting element 101 can beprevented from emitting light (bright spots can be prevented).

Although each of the first to third transistors 1405 to 1407 in FIG. 14is a P-channel transistor, the invention is not limited to this. That isto say, regardless of the conductivity of the first to third transistors1405 to 1407, the current path from the wire 1451 and the wire 1452 tothe other electrode 108 of the light emitting element 101 through eachtransistor and the light emitting element 101 can be interrupted bycutting off the portion 1401 or 1402, or both of the portion 1403 andthe portion 1404. As a result, the light emitting element 101 can beprevented from emitting light (bright spots can be prevented). Note thatanother element such as a transistor may be connected in series betweenthe wire 1451 and the first transistor 1405 in addition to the secondtransistor 1406, and another element such as a transistor may beconnected in series between the wire 1452 and the first transistor 1405in addition to the third transistor 1407. Further, another element suchas a transistor may be connected in parallel to the second transistor1406 and the third transistor 1407.

Embodiment Mode 2

Described in this embodiment mode is a method for cutting off a wire inat least one portion between one electrode of a light emitting elementand a power supply line for applying a potential to the one electrode ofthe light emitting element.

FIG. 1 shows a structure example of a pixel in a pixel portion wherepixels each having an EL element are arranged in matrix.

Each pixel has the light emitting element 101, a driving transistor 102,a switching transistor 103, and a capacitor 104. A gate electrode of theswitching transistor 103 is connected to a gate signal line (scan line)107, and one of a source and a drain of the switching transistor 103 isconnected to a source signal line (data line) 106 while the other isconnected to a gate electrode of the driving transistor 102 and oneelectrode of the capacitor 104.

The capacitor 104 is provided to hold a gate voltage of the drivingtransistor 102 (potential difference between the gate electrode and thesource) when the switching transistor 103 is not selected (off state).Note that this embodiment mode shows a structure including the capacitor104; however, the invention is not limited to this structure and thecapacitor 104 is not necessarily provided. That is to say, the gatecapacitance of the driving transistor 102 may be used instead of thecapacitor 104. The gate capacitance of the driving transistor 102 may beformed in a portion where the gate electrode overlaps the source, thedrain, an LDD region and the like, or between a channel forming regionand the gate electrode.

One of the source and the drain of the driving transistor 102 isconnected to the power supply line 105, and the other is connected toone electrode of the light emitting element 101. In this embodimentmode, the switching transistor 103 is a P-channel transistor, and thepower supply line 105 has a higher potential than the other electrode108 of the light emitting element 101. Accordingly, the source of thedriving transistor 102 is connected to the power supply line 105 and thedrain thereof is connected to one electrode of the light emittingelement 101.

The power supply line 105 is connected to the other electrode of thecapacitor 104. However, the invention is not limited to this structure,and for example, the other electrode of the capacitor 104 may beconnected to a dedicated wire or a gate signal line of another pixel.

The light emitting element 101 includes a layer containing an organiccompound, which is provided between an anode and a cathode. If the anodeis connected to the source or the drain of the driving transistor 102,the anode functions as a pixel electrode while the cathode functions asan opposite electrode. Meanwhile, if the cathode is connected to thesource or the drain of the driving transistor 102, the cathode functionsas a pixel electrode while the anode functions as an opposite electrode.In this embodiment mode, it is assumed that the anode functions as apixel electrode.

A layer containing an organic compound is formed by vapor depositionusing a deposition mask, or ink jet printing. A metal complex belongingto group 4 of the periodic table of elements is used for a part of thelayer containing an organic compound. Instead, a low molecular weightmaterial or a high molecular weight material may be used in combination.As a layer containing an organic compound, a single layer or stackedlayers are formed using an organic compound in many cases; however, aninorganic compound may be used for a part of a layer containing anorganic compound. Further, a known triplet material as well as a singletmaterial may be used.

A low power supply potential (VSS) is applied to the other electrode 108(opposite electrode (cathode)) of the light emitting element 101.Meanwhile, a high power supply potential (VDD) is applied to the powersupply line. In this specification, a high power supply potential (VDD)has a relatively higher potential than a low power supply potential(VSS). A high power supply potential and a low power supply potentialare applied by a power supply provided in a display device using anexternal IC or the like.

A method for correcting defective pixels is described.

At least one portion of a wire is cut off between the power supply line105 and the anode of the light emitting element 101. For example, atleast one of portions 121 and 122 (wire portions) each shown as anellipse in FIG. 1 is cut off. For example, an active layer of thedriving transistor 102 is cut off in the channel width direction.Accordingly, in the case of a short circuit between the two electrodesof the light emitting element, a short circuit between wires, a shortcircuit between an electrode of the light emitting element and a wire,or malfunction of the transistor connected to the light emittingelement, the current path from the power supply line 105 to the otherelectrode 108 (cathode) of the light emitting element 101 through thedriving transistor 102 and the light emitting element 101 can beinterrupted by cutting off the portion 121 or 122. As a result, thelight emitting element 101 can be prevented from emitting light (brightspots can be prevented).

The wire or the active layer may be cut off by a known method. Forexample, an interlayer insulating film on the wire or the active layeris removed by being irradiated with a laser beam with an appropriatewavelength. Then, the exposed wire or active layer is cut off by beingirradiated with a laser beam with an appropriate wavelength. Note thatirradiation conditions of laser such as the kind of laser, frequency,beam profile, energy density (or power density), and pulse width are notparticularly limited. Further, either a pulsed laser beam or acontinuous wave laser beam may be adopted. In addition, the side onwhich the light emitting element is provided (top of the substrate) maybe irradiated with a laser beam or the opposite side (bottom of thesubstrate) may be irradiated with a laser beam. If the top of thesubstrate is irradiated with a laser beam, however, it is necessary thatthe laser beam transmits the other electrode 108 (cathode) of the lightemitting element 101. Thus, the bottom of the substrate is desirablyirradiated with a laser beam.

An ultraviolet (UV) laser is used in this embodiment mode; however, thekind of laser used in the invention is not particularly limited. A laseris constituted by a laser medium, an excitation source and a resonator.A laser is classified according to medium into a gas laser, a liquidlaser and a solid laser, and classified according to the type ofoscillation into a free electron laser, a semiconductor laser and anX-ray laser. Any type of laser may be adopted in the invention. A gaslaser or a solid laser is preferably used, and more preferably, a solidlaser is used.

A gas laser includes a helium-neon laser, a carbon dioxide laser, anexcimer laser, and an argon ion laser. An excimer laser includes a raregas excimer laser and a rare gas halide excimer laser. A rare gasexcimer laser oscillates using any of three kinds of excited molecules:argon, krypton and xenon. An argon ion laser includes a rare gas ionlaser and a metal vapor ion laser.

A liquid laser includes an inorganic liquid laser, an organic chelatelaser and a pigment laser. In an inorganic liquid laser and an organicchelate laser, rare-earth ions such as neodymium, which are utilized fora solid laser, are used as a laser medium.

A laser medium used in a solid laser is a solid base doped with activespecies functioning as a laser. The solid base is crystal or glass. Thecrystal is YAG (yttrium aluminum garnet crystal), YLF, YVO₄, YAlO₃,sapphire, ruby, or alexandrite. The active species functioning as alaser are, for example, trivalent ions (Cr³⁺, Nd³⁺, Yb³⁺, Tm³⁺, Ho³⁺,Er³⁺, and Ti³⁺).

If ceramic (polycrystal) is used as a medium, a medium with a desiredshape can be formed in a short time and at low cost. The size of amedium using ceramic (polycrystal) can be larger than that of a mediumusing single crystal that is generally formed into a cylinder with adiameter of a few millimeters and a length of a few tens of millimeters.The concentration of dopant such as Nd and Yb in a medium, whichdirectly contributes to light emission, cannot be changed much in bothsingle crystal and polycrystal. Therefore, the output power of the laseris not increased much even though the concentration is increased. Ifusing ceramic as a medium, however, the output power can be expected tobe dramatically increased since the size of the medium can be made muchlarger than that using single crystal. Further, if using ceramic as amedium, a parallelepiped or rectangular parallelepiped medium can beeasily obtained. When oscillating light zigzags inside a medium havingsuch a shape, the length of the oscillating light path can be increased.As a result, the amplification is increased and oscillation with largeoutput power is achieved.

Although the driving transistor 102 is a P-channel transistor and theswitching transistor 103 is an N-channel transistor in this embodimentmode, the invention is not limited to this and both of the drivingtransistor 102 and the switching transistor 103 may be either anN-channel transistor or a P-channel transistor. If the pixel electrodefunctions as the anode of the light emitting element 101 as shown inthis embodiment mode, however, the driving transistor 102 is desirably aP-channel transistor. If the pixel electrode functions as the cathode ofthe light emitting element 101, the driving transistor 102 is desirablyan N-channel transistor since a source potential of the drivingtransistor 102 does not change and the driving transistor 102 easilyoperates.

Each of the driving transistor 102 and the switching transistor 103 mayhave an active layer formed of an amorphous semiconductor film(typically, amorphous silicon), a polycrystalline semiconductor film(typically, polysilicon), or a single crystalline semiconductor film. Ifthe driving transistor 102 is a P-channel transistor as in thisembodiment mode, the active layer is desirably formed of apolycrystalline semiconductor film in view of the mobility. Meanwhile,if the driving transistor 102 is an N-channel transistor, the activelayer is desirably formed of an amorphous semiconductor film.

Each of the driving transistor 102 and the switching transistor 103 mayhave either a forward staggered structure or an inversely staggeredstructure, and either a top gate structure or a bottom gate structure.Further, a gate electrode may be provided over or under a channelforming region.

Each of the driving transistor 102 and the switching transistor 103 mayhave either a single gate structure or a multi-gate structure. Further,each of the driving transistor 102 and the switching transistor 103 mayhave either an LDD structure or a GOLD structure.

This embodiment mode shows a structure where other transistors orelements are not provided between the driving transistor 102 and thepower supply line 105. However, similarly to the structures of FIGS. 12to 15 described in Embodiment Mode 1, the invention may be applied to apixel structure where another transistor is provided between the powersupply line and the anode in addition to the driving transistor 102.That is to say, by interrupting the current path between the anode andthe power supply line drawn into a pixel, current supply to the lightemitting element can be prevented so that the light emitting elementemits no light, and a predetermined potential can be applied to otherpixels.

Embodiment Mode 3

Described in this embodiment mode is another method for cutting off atleast one portion of a wire between one electrode of a light emittingelement and a power supply line for applying a potential to the oneelectrode of the light emitting element.

FIG. 2 shows an example of a display device. Reference numeral 201denotes a pixel portion, 202 denotes a scan line driver circuit (gatedriver), and 203 denotes a signal line driver circuit (source driver).The scan line driver circuit 202 sequentially scans each row of thepixel portion 201 through scan lines G1 to Gn (n: positive integer). Thesignal line driver circuit 203 transmits a data signal to each column ofthe pixel portion 201 through signal lines S1 to Sm (m: positiveinteger). Power supply lines V1 to Vn for applying a potential to oneelectrode of a light emitting element in each pixel have a structurecapable of applying a potential to each pixel from both the top andbottom sides. Note that the invention is not limited to the pixelstructure shown in FIG. 2, and it is needless to say that pixelstructures described in other embodiment modes may be adopted.

A method for correcting defective pixels is described with reference toFIG. 3. The pixel shown in FIG. 3 has exactly the same structure as thatshown in FIG. 1, and thus description of the connection relation and thelike is omitted.

In order not to apply a potential from the power supply line to adefective pixel, two (or three) portions (at least one of portions 131and 132 and a portion 133 in FIG. 3) of a path for applying a potentialto the pixel are cut off.

After the defective pixel is corrected, a potential can be applied fromthe bottom side through the power supply line to pixels of rows belowthe row having the defective pixel, while a potential can be appliedfrom the top side through the power supply line to pixels of rows abovethe row having the defective pixel. Thus, other pixels can operatenormally.

The invention is not limited to the pixel structure shown in FIG. 2, andcan be implemented regardless of the internal structure of pixel. Thatis to say, the invention can be applied to any pixel structure as longas a potential can be applied to each pixel from both the top and bottomsides through the power supply line 105.

Embodiment Mode 4

Described in this embodiment mode is a method for keeping a transistoroff, which is provided between a light emitting element and a powersupply line for applying a potential to the light emitting element andwhich is connected to the light emitting element.

In order to keep a transistor connected to a light emitting element off,a gate-source voltage Vgs of the transistor is controlled so thatVgs<Vth is satisfied in the case of an N-channel transistor whileVgs>Vth is satisfied in the case of a P-channel transistor. For example,when Vth>0 is satisfied in the case of an N-channel transistor or Vth<0is satisfied in the case of a P-channel transistor, a gate and a sourceof the transistor are set at the same potential.

First, description is made on the case where the light emitting element101 is connected to the power supply line 105 in the manner shown inFIG. 11. Reference numeral 1103 denotes a P-channel transistor.

In order to keep the P-channel transistor 1103 connected to the lightemitting element off, a gate-source voltage Vgs of the P-channeltransistor 1103 is controlled so that Vgs>Vth is satisfied. For example,when Vth<0 is satisfied, the gate and the source of the transistor areset at the same potential.

If one electrode of the light emitting element connected to the powersupply line is an anode, the source is connected to the power supplyline while the drain is connected to the anode. Accordingly, the gateand the source of the P-channel transistor 1103 can be set at the samepotential when the power supply line 105 is short circuited to a gatewire of the P-channel transistor 1103. As a result, even when the twoelectrodes of the light emitting element 101 are short circuited, nocurrent flows to the light emitting element 101 and a predeterminedpotential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the P-channel transistor 1103 in order to keep thetransistor connected to the light emitting element off. In other words,the gate wire of the P-channel transistor 1103 may be short circuited toa wire for applying a higher potential than the power supply line 105that is connected to a high potential power supply.

If one electrode of the light emitting element connected to the powersupply line is a cathode, the drain is connected to the power supplyline while the source is connected to the cathode. Accordingly, the gateand the source of the P-channel transistor 1103 can be set at the samepotential when the cathode of the light emitting element is shortcircuited to the gate wire of the P-channel transistor 1103. As aresult, even when the two electrodes of the light emitting element 101are short circuited, no current flows to the light emitting element 101and a predetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the P-channel transistor 1103 in order to keep thetransistor connected to the light emitting element off. In other words,the gate wire of the P-channel transistor 1103 may be short circuited toa wire for applying a higher potential than the anode of the lightemitting element that is connected to a high potential power supply.

FIG. 11 shows an example where the transistor 1103 is a P-channeltransistor. The invention can be applied to the case where thetransistor 1103 is an N-channel transistor, which is specificallydescribed below.

If one electrode of the light emitting element connected to the powersupply line is an anode, the source is connected to the one electrode ofthe light emitting element while the drain is connected to the powersupply line. Accordingly, the gate and the source of the N-channeltransistor 1103 can be set at the same potential when the one electrodeof the light emitting element is short circuited to the gate wire of theN-channel transistor 1103. As a result, even when the two electrodes ofthe light emitting element 101 are short circuited, no current flows tothe light emitting element 101 and a predetermined potential can beapplied to other pixels.

As another example, a lower potential than the source may be applied tothe gate of the N-channel transistor 1103 in order to keep thetransistor connected to the light emitting element off. In other words,the gate wire of the N-channel transistor 1103 may be short circuited toa wire for applying a lower potential than the anode of the lightemitting element.

If one electrode of the light emitting element connected to the powersupply line is a cathode, the drain is connected to the cathode whilethe source is connected to the power supply line. Accordingly, the gateand the source of the N-channel transistor 1103 can be set at the samepotential when the power supply line 105 is short circuited to the gatewire of the N-channel transistor 1103. As a result, even when the twoelectrodes of the light emitting element 101 are short circuited, nocurrent flows to the light emitting element 101 and a predeterminedpotential can be applied to other pixels.

As another example, a lower potential than the source may be applied tothe gate of the N-channel transistor 1103 in order to keep thetransistor connected to the light emitting element off. In other words,the gate wire of the N-channel transistor 1103 may be short circuited toa wire for applying a lower potential than the power supply line that isconnected to a low potential power supply.

Next, description is made on the case where the light emitting element101 is connected to the power supply line 105 in the manner shown inFIG. 12. Each of reference numerals 1204 and 1205 denotes a P-channeltransistor. Since the P-channel transistors 1204 and 1205 are connectedin series, one of them is only required to be turned off. However, bothof the P-channel transistors 1204 and 1205 may be turned off to increasereliability.

If one electrode of the light emitting element connected to the powersupply line is an anode, the source is connected to the power supplyline while the drain is connected to the anode. Accordingly, the firstP-channel transistor 1204 or the second P-channel transistor 1205 can beturned off when the power supply line 105 is short circuited to a gatewire of the first P-channel transistor 1204 or to a gate wire of thesecond P-channel transistor 1205. Alternatively, a gate and a source ofthe first P-channel transistor 1204 may be short circuited so that thefirst P-channel transistor 1204 is turned off. As a result, no currentflows to the light emitting element 101 even when the two electrodes ofthe light emitting element 101 are short circuited, thereby apredetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the first P-channel transistor 1204 or the second P-channeltransistor 1205 in order to keep the transistor connected to the lightemitting element off. In other words, the gate wire of the firstP-channel transistor 1204 or the second P-channel transistor 1205 may beshort circuited to a wire for applying a higher potential than the powersupply line 105 that is connected to a high potential power supply.

If one electrode of the light emitting element connected to the powersupply line is a cathode, the drain is connected to the power supplyline while the source is connected to the cathode. Accordingly, thefirst P-channel transistor 1204 or the second P-channel transistor 1205can be turned off when the cathode of the light emitting element isshort circuited to the gate wire of the first P-channel transistor 1204or the second P-channel transistor 1205. Alternatively, the gate and thesource of the second P-channel transistor 1205 may be short circuited sothat the second P-channel transistor 1205 is turned off. As a result,even when the two electrodes of the light emitting element 101 are shortcircuited, no current flows to the light emitting element 101 and apredetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the P-channel transistor in order to keep the transistorconnected to the light emitting element off. In other words, the gatewire of the first P-channel transistor 1204 or the second P-channeltransistor 1205 may be short circuited to a wire for applying a higherpotential than the anode of the light emitting element that is connectedto a high potential power supply.

Although FIG. 12 shows an example where each of the first transistor1204 and the second transistor 1205 is a P-channel transistor, theinvention is not limited to this. The invention can be applied to thecase where each of the first transistor 1204 and the second transistor1205 is an N-channel transistor, or only one of them is an N-channeltransistor, which is specifically described below.

Description is made on the case where each of the first transistor 1204and the second transistor 1205 is an N-channel transistor. Since theN-channel transistors 1204 and 1205 are connected in series, one of themis only required to be turned off. However, both of the N-channeltransistors 1204 and 1205 may be turned off to increase reliability.

If one electrode of the light emitting element connected to the powersupply line is an anode, the source is connected to the anode while thedrain is connected to the power supply line. Accordingly, the firstN-channel transistor 1204 or the second N-channel transistor 1205 can beturned off when the anode is short circuited to the gate wire of thefirst N-channel transistor 1204 or the second N-channel transistor 1205.Alternatively, the gate and the source of the second N-channeltransistor 1205 may be short circuited so that the second N-channeltransistor 1205 is turned off. As a result, even when the two electrodesof the light emitting element 101 are short circuited, no current flowsto the light emitting element 101 and a predetermined potential can beapplied to other pixels.

As another example, a lower potential than the source may be applied tothe gate of the first N-channel transistor 1204 or the second N-channeltransistor 1205 in order to keep the transistor connected to the lightemitting element off. In other words, the gate wire of the firstN-channel transistor 1204 or the second N-channel transistor 1205 may beshort circuited to a wire for applying a lower potential than the anode.

If one electrode of the light emitting element connected to the powersupply line is a cathode, the drain is connected to the cathode whilethe source is connected to the power supply line. Accordingly, the firstN-channel transistor 1204 or the second N-channel transistor 1205 can beturned off when the power supply line is short circuited to the gatewire of the first N-channel transistor 1204 or the second N-channeltransistor 1205. Alternatively, the gate and the source of the firstN-channel transistor 1205 may be short circuited so that the firstN-channel transistor 1205 is turned off. As a result, even when the twoelectrodes of the light emitting element 101 are short circuited, nocurrent flows to the light emitting element 101 and a predeterminedpotential can be applied to other pixels.

As another example, a lower potential than the source may be applied tothe gate of the N-channel transistor in order to keep the transistorconnected to the light emitting element off. In other words, the gatewire of the first N-channel transistor 1204 or the second N-channeltransistor 1205 may be short circuited to a wire for applying a lowerpotential than the power supply line that is connected to a lowpotential power supply.

Next, description is made on the case where one of the first transistor1204 and the second transistor 1205 is an N-channel transistor.

Since a transistor connected to a light emitting element is required tobe kept off as set forth above, at least one of the first transistor1204 and the second transistor 1205 may be kept off in FIG. 12. Themethod for keeping a transistor off in the case where the firsttransistor 1204 is a P-channel transistor or an N-channel transistor isdescribed above, and thus description thereof is omitted here.Similarly, the method for keeping a transistor off in the case where thesecond transistor 1205 is a P-channel transistor or an N-channeltransistor is described above, and thus description thereof is omittedhere.

Description is made on the case where the light emitting element 101 isconnected to the power supply line in the manner shown in FIG. 13. Eachof reference numerals 1304 and 1305 denotes a P-channel transistor.

If the potential of the other electrode 108 of the light emittingelement is lower than those of a wire 1351 and a wire 1352 and oneelectrode of the light emitting element connected to a power supply lineis an anode, a source is connected to the power supply line while adrain is connected to the anode. Accordingly, a gate and the source ofthe first P-channel transistor 1304, and a gate and the source of thesecond P-channel transistor 1305 can be set at the same potential whenthe wire 1351 is short circuited to a gate wire of the first P-channeltransistor 1304 and the wire 1352 is short circuited to a gate wire ofthe second P-channel transistor 1305. As a result, even when the twoelectrodes of the light emitting element 101 are short circuited, nocurrent flows to the light emitting element 101 and a predeterminedpotential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the first P-channel transistor 1304 and the gate of thesecond P-channel transistor 1305 in order to keep the transistorsconnected to the light emitting element off. In other words, the gatewire of the first P-channel transistor 1304 may be short circuited to awire for applying a higher potential than the wire 1351 that isconnected to a high potential power supply, and the gate wire of thesecond P-channel transistor 1305 may be short circuited to a wire forapplying a higher potential than the wire 1352 that is connected to ahigh potential power supply.

If one electrode of the light emitting element connected to the powersupply line is a cathode, the drain is connected to the power supplyline while the source is connected to the cathode. Accordingly, the gateand the source of the first and second P-channel transistors can be setat the same potential when the cathode of the light emitting element isshort circuited to the gate wires of the first P-channel transistor 1304and the second P-channel transistor 1305. As a result, even when the twoelectrodes of the light emitting element 101 are short circuited, nocurrent flows to the light emitting element 101 and a predeterminedpotential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the first P-channel transistor 1304 and the gate of thesecond P-channel transistor 1305 in order to keep the transistorsconnected to the light emitting element off. In other words, the gatewires of the first P-channel transistor 1304 and the second P-channeltransistor 1305 may be short circuited to a wire for applying a higherpotential than the anode of the light emitting element that is connectedto a high potential power supply.

Although FIG. 13 shows the case where each of the first transistor 1304and the second transistor 1305 is a P-channel transistor, the inventionis not limited to this. The invention can be applied to the case whereeach of the first transistor 1304 and the second transistor 1305 is anN-channel transistor, or only one of them is an N-channel transistor.

Next, description is made on the case where the light emitting element101 is connected to the power supply line in the manner shown in FIG.14. Each of reference numerals 1405, 1406 and 1407 denotes a P-channeltransistor.

If the potential of the other electrode 108 of the light emittingelement is lower than those of a wire 1451 and a wire 1452 and oneelectrode of the light emitting element connected to the power supplyline is an anode, a source is connected to the power supply line while adrain is connected to the anode. Accordingly, a gate and the source ofthe second P-channel transistor 1406, and a gate and the source of thethird P-channel transistor 1407 can be set at the same potential whenthe wire 1451 is short circuited to a gate wire of the second P-channeltransistor 1406 and the wire 1452 is short circuited to a gate wire ofthe third P-channel transistor 1407. Further, a gate and the source ofthe first P-channel transistor 1405 can be set at the same potentialwhen a gate wire of the first P-channel transistor 1405 is shortcircuited to a wire for connecting the first P-channel transistor 1405to the second and third P-channel transistors 1406 and 1407.Alternatively, the gate wire of the first P-channel transistor 1405 maybe short circuited to the wire 1451 or the wire 1452. As a result, evenwhen the two electrodes of the light emitting element 101 are shortcircuited, no current flows to the light emitting element 101 and apredetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the second P-channel transistor 1406 and the gate of thethird P-channel transistor 1407 in order to keep the transistorsconnected to the light emitting element off. In other words, the gatewire of the second P-channel transistor 1406 may be short circuited to awire for applying a higher potential than the wire 1451 that isconnected to a high potential power supply, and the gate wire of thethird P-channel transistor 1407 may be short circuited to a wire forapplying a higher potential than the wire 1452 that is connected to ahigh potential power supply. For example, if the potential of the wire1452 is higher than that of the wire 1451, the wire 1452 may be shortcircuited to the gate wire of the second P-channel transistor 1406.Instead, a higher potential than the source may be applied to the gateof the first P-channel transistor 1405.

If one electrode of the light emitting element connected to the powersupply line is a cathode, a drain is connected to the power supply linewhile a source is connected to the cathode. Accordingly, the gate andthe source of the first P-channel transistor 1405 can be set at the samepotential when the cathode of the light emitting element is shortcircuited to the gate wire of the first P-channel transistor 1405.Further, the gate and the source of the second P-channel transistor 1406and the gate and the source of the third P-channel transistor 1407 canbe set at the same potential when both the gate wire of the secondP-channel transistor 1406 and the gate wire of the third P-channeltransistor 1407 are short circuited to a wire for connecting the firstP-channel transistor 1405 to the second and third P-channel transistors1406 and 1407. Alternatively, the gate of the first P-channel transistor1405 may be short circuited to the wire 1451 or the wire 1452 so thatthe first P-channel transistor 1405 is turned off. As a result, evenwhen the two electrodes of the light emitting element 101 are shortcircuited, no current flows to the light emitting element 101 and apredetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the second P-channel transistor 1406 and the gate of thethird P-channel transistor 1407 in order to keep the transistorsconnected to the light emitting element off. Instead, a higher potentialthan the source may be applied to the gate of the first P-channeltransistor 1405.

Although FIG. 14 shows the case where each of the first to thirdtransistors 1405 to 1407 is a P-channel transistor, the invention is notlimited to this. The invention can be applied to the case where each ofthe first to third transistors 1405 to 1407 is an N-channel transistor,or one or two of them are N-channel transistors.

Next, description is made on the case where the light emitting element101 is connected to the power supply line in the manner shown in FIG.15. Each of reference numerals 1506, 1507 and 1508 denotes a P-channeltransistor.

If the potential of the other electrode 108 of the light emittingelement is lower than those of a wire 1551 and a wire 1552 and oneelectrode of the light emitting element connected to the power supplyline is an anode, a source is connected to the power supply line while adrain is connected to the anode. Accordingly, a gate and the source ofthe second P-channel transistor 1507, and a gate and the source of thethird P-channel transistor 1508 can be set at the same potential whenthe wire 1551 is short circuited to a gate wire of the second P-channeltransistor 1507 and the wire 1552 is short circuited to a gate wire ofthe third P-channel transistor 1508. Further, a gate and the source ofthe first P-channel transistor 1506 can be set at the same potentialwhen a gate wire of the first P-channel transistor 1506 is shortcircuited to the wire 1551 or a wire for connecting the first P-channeltransistor 1506 to the second P-channel transistor 1507. As a result,even when the two electrodes of the light emitting element 101 are shortcircuited, no current flows to the light emitting element 101 and apredetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the first P-channel transistor 1506 or the second P-channeltransistor 1507 and the gate of the third P-channel transistor 1508 inorder to keep the transistors connected to the light emitting elementoff. In other words, the gate wire of the first P-channel transistor1506 or the second P-channel transistor 1507 may be short circuited to awire for applying a higher potential than the wire 1551 that isconnected to a high potential power supply, and the gate wire of thethird P-channel transistor 1508 may be short circuited to a wire forapplying a higher potential than the wire 1552 that is connected to ahigh potential power supply.

If one electrode of the light emitting element connected to the powersupply line is a cathode, a drain is connected to the power supply linewhile a source is connected to the cathode. Accordingly, the currentpath between the wire 1551 and the anode of the light emitting element101 can be interrupted when the cathode of the light emitting element isshort circuited to the gate wire of the first P-channel transistor 1506,or the gate wire of the second P-channel transistor 1507 is shortcircuited to a wire for connecting the first P-channel transistor 1506to the second P-channel transistor 1507. Further, the current pathbetween the wire 1552 and the anode of the light emitting element 101can be interrupted when the cathode of the light emitting element isshort circuited to the gate wire of the third P-channel transistor 1508.As a result, even when the two electrodes of the light emitting element101 are short circuited, no current flows to the light emitting element101 and a predetermined potential can be applied to other pixels.

As another example, a higher potential than the source may be applied tothe gate of the first P-channel transistor 1506 or the gate of thesecond P-channel transistor 1507 and a higher potential than the sourcemay be applied to the gate of the third P-channel transistor 1508, sothat the transistors connected to the light emitting element are keptoff.

Although FIG. 15 shows the case where each of the first to thirdtransistors 1506 to 1508 is a P-channel transistor, the invention is notlimited to this. The invention can be applied to the case where each ofthe first to third transistors 1506 to 1508 is an N-channel transistor,or one or two of them are N-channel transistors.

Described in this embodiment mode is a method for keeping a transistorconnected to a light emitting element off. If there are a plurality ofcurrent paths for applying a potential to a light emitting element, themethod described in this embodiment mode can be combined with themethods described in Embodiment Modes 1 and 2. For example, in FIG. 15,the current path connected to the wire 1551 may be interrupted bycutting off a portion 1502 or a portion 1504 by laser irradiation, whilethe current path connected to the wire 1552 may be interrupted bykeeping the third transistor 1508 off by setting the gate and the sourceof the third transistor 1508 at the same potential.

Embodiment Mode 5

Described in this embodiment mode is a method for keeping a transistoroff, which is provided between a light emitting element and a powersupply line for applying a potential to the light emitting element andwhich is connected to the light emitting element. Description is madewith reference to FIG. 4 that is the same as FIG. 1, except in that theswitching transistor 103 is a P-channel transistor. Thus, description ofthe connection relation and the like is omitted here.

As described in Embodiment Mode 1, the driving transistor 102 is aP-channel transistor, and one electrode of the light emitting elementconnected to the power supply line is an anode. That is to say, a sourceis connected to the power supply line while a drain is connected to theanode. Accordingly, more specifically, the gate and the source of thedriving transistor 102 can be set at the same potential when the powersupply line 105 is short circuited to the gate wire of the drivingtransistor 102. As a result, even when the two electrodes of the lightemitting element 101 are short circuited, no current flows to the lightemitting element 101 and a predetermined potential can be applied toother pixels. Note that the driving transistor 102 having the gate andthe source that are at the same potential is desirably an enhancementtransistor.

As another example, a higher potential than the source may be applied tothe gate of the P-channel driving transistor 102 in order to keep thetransistor connected to the light emitting element off. In other words,the gate wire of the driving transistor 102 may be short circuited to awire for applying a higher potential than the power supply line 105 thatis connected to a high potential power supply. This method isspecifically described below.

Since the switching transistor 103 is a P-channel transistor in thisembodiment mode, a Hi (High) signal is normally inputted to the gatesignal line 107 connected to the gate of the switching transistor 103,so that the switching transistor 103 is turned off. Accordingly, thedriving transistor 102 can be forcibly turned off when a higherpotential than the power supply line 105 is applied to the gate signalline 107 and the gate signal line 107 is short circuited to the gatewire of the driving transistor 102.

The gate signal line 107 and the gate wire of the driving transistor 102may be short circuited by a known method. For example, a portion wherethe gate signal line 107 overlaps the gate wire of the drivingtransistor 102 with an insulating film interposed therebetween isirradiated with a laser beam having an appropriate wavelength. Theinsulating film in this portion is destroyed by laser irradiation,thereby the gate signal line 107 can be connected to the gate wire ofthe driving transistor 102 in the vicinity of the portion irradiatedwith the laser beam. Note that irradiation conditions of laser such asthe kind of laser, energy density and pulse width are not particularlylimited. Further, either a pulsed laser beam or a continuous wave laserbeam may be adopted. In addition, the side on which the light emittingelement is provided (top of the substrate) may be irradiated with alaser beam or the opposite side (bottom of the substrate) may beirradiated with a laser beam. If the top of the substrate is irradiatedwith a laser beam, however, it is necessary that the laser beamtransmits the cathode 108; therefore, the bottom of the substrate isdesirably irradiated with a laser beam.

As described in Embodiment Mode 1 with reference to FIGS. 12 to 15,another transistor may be provided between the power supply line and theanode in addition to the driving transistor 102. In that case also, atleast one of the transistors connected between the power supply line andthe anode is kept off using the method shown in this embodiment mode, sothat no current flows to one electrode of the light emitting element.

Although the driving transistor 102 is a P-channel transistor in thisembodiment mode, this method can be applied to the case where thedriving transistor 102 is an N-channel transistor.

Although the switching transistor 103 is a P-channel transistor in thisembodiment mode, this method can be applied to the case where theswitching transistor 103 is an N-channel transistor.

Embodiment Mode 6

Described in this embodiment mode is a structure of a pixel portion of adisplay device where defective pixels can be easily corrected.

FIG. 17 shows a layout example of one pixel. A magnified view of aportion surrounded by a dotted line in FIG. 17 is shown in FIG. 5A. FIG.5B is a cross sectional view along a line A-A′ of FIG. 5A. Note that anequivalent circuit of this pixel corresponds to FIG. 1.

In FIGS. 5A and 5B, reference numeral 501 denotes one electrode (anode)of a light emitting element, 502 denotes a wire, 503 denotes an activelayer of the driving transistor 102, 504 denotes a gate wire alsofunctioning as a gate electrode of the driving transistor 102, 521denotes a substrate, 522 denotes a base film, 523 denotes a gateinsulating film of the driving transistor 102, 524 denotes an interlayerinsulating film, and 525 denotes an interlayer insulating film. Theseelements may be formed of known materials. Although the materials arespecifically shown below, the invention is not limited to these.

The substrate 521 may be a glass substrate such as barium borosilicateglass and alumino borosilicate glass, a quartz substrate, a ceramicsubstrate, a substrate formed of a flexible synthetic resin such asplastic, or the like.

The base film 522 may have a single layer structure using any one of asilicon oxide film, a silicon nitride film, a silicon oxynitride film,and a silicon nitride oxide film, or a stacked layer structure of any ofthem. For example, as the base film 522, a silicon nitride oxide filmand a silicon oxynitride film may be stacked in this order over thesubstrate 521. In that case, the base film 522 may be transparent andcan transmit a laser beam. Accordingly, only a wire or a semiconductorlayer formed over the base film can be cut off or wires can be shortcircuited. Note that in this specification, silicon oxynitride means asubstance where the composition ratio of oxygen is higher than that ofnitrogen, which can also be referred to as silicon oxide containingnitrogen. Meanwhile, in this specification, silicon nitride oxide meansa substance where the composition ratio of nitrogen is higher than thatof oxygen, which can also be referred to as silicon nitride containingoxygen.

The active layer 503 may be formed of an amorphous semiconductor film, amicrocrystalline semiconductor film, a crystalline semiconductor film orthe like. The material of the semiconductor film is not limited;however, silicon or silicon germanium (SiGe) is preferably used. Theactive layer 503 of the driving transistor 102 has at least a source, adrain and a channel forming region, and each of the source and the draincontains an impurity that imparts P-type conductivity. The active layer503 may have a structure where a gate electrode overlaps an LDD region,a structure where a gate electrode does not overlap an LDD region, or anoffset structure. For example, the driving transistor 102 preferably hasa structure where a gate electrode overlaps an LDD region in each caseof an N-channel transistor and a P-channel transistor. Meanwhile, theswitching transistor 103 preferably has a structure where a gateelectrode does not overlap an LDD region in each case of an N-channeltransistor and a P-channel transistor.

The gate insulating film 523 may have a single layer structure using anyone of a silicon oxide film, a silicon nitride film, a siliconoxynitride film, and a silicon nitride oxide film, or a stacked layerstructure of any of them. For example, the gate insulating film 523 mayhave a single layer structure using a silicon oxide film, or a stakedlayer structure where a silicon oxynitride film and a silicon nitrideoxide film are stacked in this order.

The gate wire 504 may be formed of a metal such as Al, Mo, Ti, Nd, andW, an alloy thereof, or a metal nitride thereof. The gate wire 504 mayhave a signal layer structure using any of these metals, or a stackedlayer structure of any of them. In addition, a polysilicon film may beformed as a conductive film.

The interlayer insulating film 524 may have a single layer structureusing any one of a silicon oxide film, a silicon nitride film, a siliconoxynitride film, and a silicon nitride oxide film, or a stacked layerstructure of any of them. If the gate wire 504 is formed of molybdenum(Mo), a silicon nitride film is preferably used for the interlayerinsulating film 524 that is in contact with the gate wire 504.

The wire 502 and the power supply line 105 are formed of a metal such asAg, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba,and Nd, an alloy thereof, or a metal nitride thereof. Alternatively, asemiconductor material such as Si and Ge may be employed. Each of thewire 502 and the power supply line 105 may have a stacked layerstructure of these materials. Note that a metal material with a lowmelting point is suitable for the wire 502 and the power supply line 105in the invention, since the wire 502 and the power supply line 105 canbe easily cut off by laser irradiation in subsequent steps.

The interlayer insulating film 525 may be formed of an inorganicinsulating material such as silicon oxide, silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, and aluminum oxynitride;acrylic acid, methacrylic acid, and a derivative thereof; a heatresistance polymer such as polyimide, aromatic polyamide, andpolybenzimidazole; inorganic siloxane including a Si—O—Si bond, amongcompounds formed of silicon, oxygen and hydrogen using a siloxane-basedmaterial as a start material; or an organic siloxane-based insulatingmaterial in which hydrogen bonded to silicon is substituted by anorganic group such as a methyl group and a phenyl group. The interlayerinsulating film 525 may also be formed of a photosensitive ornon-photosensitive material such as acrylic and polyimide, or formed bystacking these materials. It is also possible to adopt a structure shownin FIG. 16, where the interlayer insulating film 525 is not provided andthe one electrode 501 of the light emitting element is connecteddirectly to the wire 502 without through a contact hole.

A structure of a display device in this embodiment mode is described.

Since the power supply line 105 is connected to the driving transistor102 through a contact hole, a part of the power supply line 105 has aprojecting portion for each pixel (row). In the portion where a part ofthe power supply line projects, the width of a part of the power supplyline is reduced (portion 515 in FIG. 5). In that case, the longitudinalwidth (Y55) of the power supply line 105 in the portion 515 ispreferably 3 μm or less. In addition, the horizontal width (X55) of thepower supply line 105 in the portion 515 is preferably 4 μm or more. Asa result, only a portion required for correcting defects can be cut offin view of the size and shape of a cross sectional surface (spot) of alaser shot, and thus the power supply line 105 itself can be preventedfrom being broken and adversely affecting other pixels. Further, otherwires can also be prevented from being short circuited and adverselyaffecting other circuits.

When the power supply line 105 is formed into such a shape, the powersupply line 105 can be easily cut off when the portion 515 is irradiatedwith a laser beam. In other words, in any defective pixel, only a defectcan be easily corrected without adversely affecting other pixels.

The active layer 503 of the driving transistor 102 has portions 513 and514 that are not covered with the wire 502, the gate wire 504 and thepower supply line 105. The active layer 503 may be cut off by reducingthe length of the portions 513 and 514 in a direction parallel to thechannel width of the driving transistor 102 and irradiating the portion513 or 514 with a laser beam. In that case, the lengths (Y53 and Y54) ofthe portions in a direction parallel to the channel width of the drivingtransistor 102 are preferably 3 μm or less. In addition, the lengths(X53 and X54) of the portions in a direction parallel to the channellength of the driving transistor 102 are preferably 4 μm or more.

The width of a part of the wire 502 for connecting the active layer 503to the one electrode (anode) 501 of the light emitting element may bereduced between a contact hole for connecting the wire 502 to the activelayer 503 and a contact hole for connecting the wire 502 to the oneelectrode (anode) 501 of the light emitting element. In that case, thelongitudinal width (Y52) of a part of the wire 502 is preferably 3 μm orless. In addition, the horizontal width (X52) of a part of the wire 502is preferably 4 μm or more.

When the wire 502 is formed into such a shape, the wire 502 can beeasily cut off when a portion 512 is irradiated with a laser beam. Inother words, in any defective pixel, only a defect can be easilycorrected without adversely affecting other pixels.

The width of a part of the one electrode (anode) 501 of the lightemitting element can be reduced in a portion adjacent to the portionwhere the one electrode 501 of the light emitting element overlaps thewire 502. In that case, the longitudinal width (Y51) of a part of theone electrode (anode) 501 of the light emitting element is preferably 3μm or less. In addition, the horizontal width (X51) of a part of the oneelectrode (anode) 501 of the light emitting element is preferably 4 μmor more.

When the one electrode (anode) 501 of the light emitting element isformed into such a shape, the one electrode (anode) 501 of the lightemitting element can be easily cut off by irradiating a portion 511 witha laser beam. In other words, in any defective pixel, only a defect canbe easily corrected without adversely affecting other pixels.

Although FIG. 5 shows a structure where the gate electrode is providedover the semiconductor active layer (top gate structure), at least oneof the portions 511 to 515 can be easily cut off by laser irradiationeven when adopting a structure where the gate electrode is providedunder the semiconductor active layer as shown in FIG. 9.

The invention can also be applied to the case of adopting a bottom gatetransistor where amorphous silicon is used for a semiconductor layer. Atleast one of the portions 511 to 515 can be easily cut off by laserirradiation even when adopting, for example, an inversely staggeredchannel etched transistor as shown in FIG. 19, or a channel protectivetransistor as shown in FIG. 20. Note that in FIG. 20, an insulating film516 functions as a film for protecting a channel.

Embodiment Mode 7

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 6 is a top plan view of a layout of one pixel. Note that anequivalent circuit of this pixel structure corresponds to FIG. 1.

The active layer 503 of the driving transistor 102 has a portion 612that is not covered with the wire 502 and the power supply line 105. Theactive layer 503 may be cut off by reducing the length of the portion612 in a direction parallel to the power supply line 105 and irradiatingthe portion 612 with a laser beam. In that case, the length (Y62) of theportion in a direction parallel to the power supply line 105 ispreferably 3 μm or less. In addition, the length (X62) of the portion ina direction perpendicular to the power supply line 105 is preferably 4μm or more. As a result, only a portion required for correcting defectscan be cut off in view of the size and shape of a cross sectionalsurface (spot) of a laser shot, and thus the power supply line 105itself can be prevented from being broken and adversely affecting otherpixels. Further, other wires can be prevented from being short circuitedand adversely affecting other pixels.

The width of a part of the wire 502 for connecting the active layer 503to the one electrode (anode) 501 of the light emitting element may bereduced between a contact hole for connecting the wire 502 to the activelayer 503 and a contact hole for connecting the wire 502 to the oneelectrode (anode) 501 of the light emitting element. In that case, thelongitudinal width (Y61) of a part of the wire 502 is preferably 3 μm orless. In addition, the horizontal width (X61) of a part of the wire 502is preferably 4 μm or more.

When the wire 502 is formed into such a shape, the wire 502 can beeasily cut off by irradiating a portion 611 with a laser beam. In otherwords, in any defective pixel, only a defect can be easily correctedwithout adversely affecting other pixels.

Embodiment Mode 8

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 7 is a top plan view of a layout of one pixel. Note that anequivalent circuit of this pixel structure corresponds to FIG. 1, andthe driving transistor 102 is a P-channel transistor. It is assumed thatthe source of the driving transistor 102 is connected to the powersupply line 105 and the drain thereof is connected to the one electrode(anode) 501 of the light emitting element.

The power supply line 105 has a substantially linear shape, but has adepressed portion for each pixel (row). Further, a part of the depressedportion projects to be connected to the active layer 503, and the widthof a part of the projection portion is reduced. In that case, thelongitudinal width (Y72) of the power supply line 105 in a portion 712is preferably 3 μm or less. In addition, the horizontal width (X72) ofthe power supply line 105 in the portion 712 is preferably 4 μm or more.

When the power supply line 105 is formed into such a shape, the powersupply line 105 can be easily cut off by irradiating the portion 712with a laser beam. In other words, in any defective pixel, only a defectcan be easily corrected without adversely affecting other pixels. In thestructure shown in FIG. 5, a layout area is increased as a part of thepower supply line 105 projects, which leads to reduced aperture ratio.Meanwhile, in the structure shown in FIG. 7 where the power supply linehas the depressed portion, the wire 502 can be easily cut off withoutreducing aperture ratio.

The gate wire 504 overlaps the power supply line 105 with an interlayerinsulating film interposed therebetween. The gate wire 504 may be shortcircuited to the power supply line 105 by irradiating a part of theoverlapping area, for example a portion 713, with a laser beam. That isto say, the gate and the source of the driving transistor 102 have thesame potential when the gate wire 504 is short circuited to the powersupply line 105; therefore, the driving transistor 102 is turned off, nocurrent flows even when the light emitting element is short circuited,and a defective pixel can be easily corrected.

The active layer 503 of the driving transistor 102 has portions 721 and722 that are not covered with the wire 502, the gate wire 504 and thepower supply line 105. The active layer 503 may be cut off by reducingthe length of the portions 721 and 722 in a direction parallel to thechannel width of the driving transistor 102 and irradiating the portion721 or 722 with a laser beam. In that case, the lengths (Y73 and Y74) ofthe portion in a direction parallel to the channel width of the drivingtransistor 102 are preferably 3 μm or less. In addition, the lengths(X73 and X74) of the portion in a direction parallel to the channelwidth of the driving transistor 102 are preferably 4 μm or more.

The width of a part of the wire 502 for connecting the active layer 503to the one electrode (anode) 501 of the light emitting element may bereduced between a contact hole for connecting the wire 502 to the activelayer 503 and a contact hole for connecting the wire 502 to the oneelectrode (anode) 501 of the light emitting element. In that case, thelongitudinal width (Y71) of a part of the wire 502 is preferably 3 μm orless. In addition, the horizontal width (X71) of a part of the wire 502is preferably 4 μm or more.

When the wire 502 is formed into such a shape, the wire 502 can beeasily cut off by irradiating the portion 711 with a laser beam. Lnother words, in any defective pixel, only a defect can be easilycorrected without adversely affecting other pixels.

Embodiment Mode 9

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 18 is a top plan view of a layout of one pixel. Note that anequivalent circuit of this pixel structure corresponds to FIG. 13 in thecase where the wire 1351 and the wire 1352 are connected to the samepower supply. The one electrode 501 of the light emitting element isconnected to the power supply line 105 through a first transistor and asecond transistor that are connected in parallel to each other.

The power supply line 105 has a substantially linear shape, but has twoprojecting portions for each pixel (row). Further, the width of a partof the projecting portions is reduced. In that case, the longitudinalwidth (Y) of the power supply line 105 in a portion 1801 and a portion1805 is preferably 3 μm or less. In addition, the horizontal width (X)of the power supply line 105 in the portion 712 is preferably 4 μm ormore.

When the power supply line 105 is formed into such a shape, the powersupply line 105 can be easily cut off by irradiating the portion 1801and the portion 1805 with a laser beam. In other words, in any defectivepixel, only a defect can be easily corrected without adversely affectingother pixels.

The gate wire 504 overlaps the power supply line 105 with an interlayerinsulating film interposed therebetween. Accordingly, if each of thefirst transistor and the second transistor is a P-channel transistor andthe one electrode 501 of the light emitting element is an anode, or ifeach of the first transistor and the second transistor is an N-channeltransistor and the one electrode 501 of the light emitting element is acathode, the gate wire 504 may be short circuited to the power supplyline 105 by irradiating a part of an area where the gate wire 504overlaps the power supply line 105, for example a portion 1808, with alaser beam. That is to say, the gate and the source of each of the firsttransistor and the second transistor have the same potential when thegate wire 504 is short circuited to the power supply line 105;therefore, each of the transistors is turned off, no current flows evenwhen the light emitting element is short circuited, and a defectivepixel can be easily corrected.

The active layer 503 of the first and second transistors may be cut offby irradiating both a portion 1802 and a portion 1804 with a laser beam.Since one portion is only required to be irradiated with a laser beam, aportion 1803 is preferably irradiated with a laser beam to increaseyield. Note that the horizontal width (X) of the portion 1802 and theportion 1804 is preferably 3 μm or less, and the longitudinal width (Y)thereof is preferably 4 μm or more.

When the active layer 503 is formed into such a shape, the active layer503 can be easily cut off by irradiating both of the portion 1802 andthe portion 1804, or the portion 1803 with a laser beam. In other words,in any defective pixel, only a defect can be easily corrected withoutadversely affecting other pixels.

Although the one electrode 501 of the light emitting element isconnected directly to the active layer 503 of the first and secondtransistors in FIG. 18, a wire 1806 may be provided between the oneelectrode 501 of the light emitting element and the active layer 503 ofthe first and second transistors as shown in FIG. 35. In that case, thewire 1806 can be formed simultaneously with the power supply line 105.In addition, the wire 1806 has a structure capable of easily correctingdefective pixels. That is to say, the width of a part of the wire 1806is reduced between a portion where the one electrode 501 of the lightemitting element is connected to the wire 1806 and a portion where thewire 1806 is connected to the active layer 503 of the first and secondtransistors. The width of a portion 1807 where the width of the wire1806 is reduced is preferably 3 μm or less.

Embodiment Mode 10

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 36A shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 36A is a top plan view showing theconnection relation between a pixel electrode (one of a pair ofelectrodes of a light emitting element) and a power supply line, andFIG. 36B is a cross sectional view along a line A-A′ of FIG. 36A. Anequivalent circuit of the top plan view shown in FIG. 36A corresponds toFIG. 12. In other words, FIGS. 36A and 36B have a structure where twotransistors connected in series are provided between the pixel electrode(one of a pair of electrodes of the light emitting element) and thepower supply line.

FIG. 36A has almost the same structure as FIG. 5A described inEmbodiment Mode 6, except in that there are two overlapping areas of thegate wire 504 and the active layer 503 of the driving transistor in FIG.36A while there is one overlapping area in FIG. 5A. Therefore, in thisembodiment mode, only the difference from FIG. 5 is described. In thisembodiment mode, the width (Y54) of the active layer 503 that issandwiched between two gate wires when seen from the top surface isreduced. The width of the active layer 503 in this portion is preferably3 μm or less.

In the display device having the active layer 503 formed into such ashape, defects in any pixel can be easily corrected without adverselyaffecting other pixels.

Embodiment Mode 11

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 37A shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 37A is a top plan view showing theconnection relation between a pixel electrode (one of a pair ofelectrodes of a light emitting element) and a power supply line, andFIG. 37B is a cross sectional view along a line A-A′ of FIG. 37A. Anequivalent circuit of the top plan view shown in FIG. 37A corresponds toFIG. 12, and similarly to FIG. 36A, FIG. 37A has a structure where twotransistors connected in series are provided between a pixel electrode(one of a pair of electrodes of a light emitting element) and a powersupply line.

FIG. 37A has almost the same structure as FIG. 36A, except in that theactive layer 503 described in Embodiment Mode 10 with reference to FIG.36A is divided into two layers that are connected through the wire 531.Therefore, in this embodiment mode, only the difference from FIG. 36A isdescribed. In this embodiment mode, the widths (Y56 and Y58) of theactive layer 503 that is sandwiched between two gate wires when seenfrom the top surface and that does not overlap the wire 531 are reduced.The width of the active layer 503 in this portion is preferably 3 μm orless. One or both of the width Y56 and the width Y58 of the active layer503 may be reduced.

Instead of reducing the width of at least a part of the active layer503, the width of the wire 531 in a portion where the wire 531 does notoverlap two active layers when seen from the top surface may be reduced.The width Y57 of the wire 531 in this portion is preferably 3 μm orless.

In the display device having the active layer 503 or the wire 531 formedinto such a shape, defects in any pixel can be easily corrected withoutadversely affecting other pixels.

Embodiment Mode 12

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 38 shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 38 is a top plan view showing theconnection relation between a pixel electrode and a power supply line.An equivalent circuit of the top plan view shown in FIG. 38 correspondsto FIG. 13, and has a structure where at least two transistors connectedto one electrode of a light emitting element are provided between apixel electrode (one of a pair of electrodes of the light emittingelement) and a power supply line.

In FIG. 38, one of the source and the drain of the transistor 1304having an active layer 1365 is connected through a wire 1362 to one ofthe source and the drain of the transistor 1305 having an active layer1366. The wire 1362 is connected to one electrode 1361 (pixel electrode)of the light emitting element 101. The other of the source and the drainof the transistor 1304 is connected to a wire 1351, and the other of thesource and the drain of the transistor 1305 is connected to a wire 1352.

In this embodiment mode, the widths Y103 and Y104 of the active layer1365 that does not overlap the wire 1362, a gate wire 1363 and the wire1351, or the width Y107 of the wire 1351 that does not overlap theactive layer 1365 is reduced. In that case, the widths Y103 and Y104 ofthe active layer 1365, or the width Y107 of the wire 1351 is preferably3 μm or less. All of the widths Y103, Y104 and Y107 may be reduced, orat least one of them may be reduced.

In this embodiment mode, the widths Y105 and Y106 of the active layer1366 that does not overlap the wire 1362, a gate wire 1364 and the wire1352, or the width Y108 of the wire 1352 that does not overlap theactive layer 1366 is reduced. In that case, the widths Y105 and Y106 ofthe active layer 1366, or the width Y108 of the wire 1352 that does notoverlap the active layer 1366 is preferably 3 μm or less. All of thewidths Y105, Y106 and Y108 may be reduced, or at least one of them maybe reduced.

Instead of reducing both of the widths Y103, Y104 and Y107 and thewidths Y105, Y106 and Y108, the width Y101 of the wire 1362 in thevicinity of a portion where the one electrode 1361 of the light emittingelement 101 does not overlap the wire 1362 when seen from the topsurface, or the width Y102 of the one electrode 1361 of the lightemitting element 101 may be reduced. The latter structure is preferablyadopted instead of the former structure, since defective pixels can becorrected by cutting off only one portion of a wire and the like. Thewidth Y101 of the wire 1362 or the width Y102 of the one electrode 1361of the light emitting element 101 is preferably 3 μm or less.

In the display device having the one electrode 1361 of the lightemitting element 101, the wire 1362, the active layer 1365, the activelayer 1366, the wire 1351, and the wire 1352 that are formed into such ashape, defects in any pixel can be easily corrected without adverselyaffecting other pixels.

Embodiment Mode 13

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 39 shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 39 is a top plan view showing theconnection relation between a pixel electrode (one of a pair ofelectrodes of a light emitting element) and a power supply line. Anequivalent circuit of the top plan view shown in FIG. 39 corresponds toFIG. 13, and similarly to FIG. 38, FIG. 39 has a structure where twotransistors are connected to one electrode of a light emitting element.

FIG. 39 has almost the same structure as that described in EmbodimentMode 10 with reference to FIG. 38, except in that the two active layers1365 and 1366 are substituted by one active layer 1372. Therefore, inthis embodiment mode, only the difference from FIG. 38 is described. Inthis embodiment mode, both of the widths Y113 and Y114 and the widthsY115 and Y116 may be reduced. Alternatively, the width Y111 or Y112 maybe reduced. The latter structure is preferably adopted instead of theformer structure, since defective pixels can be corrected by cutting offonly one portion of a wire and the like. Each of the widths Y103, Y104,Y107, Y105, Y106, and Y108 is preferably 3 μm or less.

In the display device having the one electrode 1361 of the lightemitting element 101, the wire 1371, the active layer 1372, the wire1351, and the wire 1352 that are formed into such a shape, defects inany pixel can be easily corrected without adversely affecting otherpixels.

Embodiment Mode 14

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 40 shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 40 is a top plan view showing theconnection relation between a pixel electrode and a power supply line.An equivalent circuit of the top plan view shown in FIG. 40 correspondsto FIG. 14, and has a structure including at least the transistor 1405connected to one electrode of a light emitting element and the twotransistors 1406 and 1407 connected to the transistor 1405.

In FIG. 40, one of the source and the drain of the transistor 1406having an active layer 1468 is connected to one of the source and thedrain of the transistor 1407 having an active layer 1469 through a wire1465. The wire 1465 is connected to one of the source and the drain ofthe transistor 1405 having an active layer 1464. The other of the sourceand the drain of the transistor 1405 is connected to one electrode 1461(pixel electrode) of the light emitting element 101 through a wire 1462.The other of the source and the drain of the transistor 1406 isconnected to a wire 1451, and the other of the source and the drain ofthe transistor 1407 is connected to a wire 1452.

In this embodiment mode, as described in Embodiment Mode 13 withreference to FIG. 39, at least one of the widths Y126, Y127 and Y128,and at least one of the widths Y129, Y130 and Y131 are reduced. In thatcase, at least one of the widths Y126, Y127 and Y128, and at least oneof the widths Y129, Y130 and Y131 are preferably 3 μm or less.

Instead of reducing at least one of the widths Y126, Y127 and Y128, andat least one of the widths Y129, Y130 and Y131, at least one of thewidths Y121, Y122, Y123, Y124, and Y125 may be reduced. The latterstructure is preferably adopted instead of the former structure, sincedefective pixels can be corrected by cutting off only one portion of awire and the like. In that case, each of the widths Y121, Y122, Y123,Y124, and Y125 is preferably 3 μm or less.

In the display device having the one electrode 1461 of the lightemitting element 101, the wire 1462, the active layer 1464, the wire1465, the active layer 1468, the active layer 1469, the wire 1451, andthe wire 1452 that are formed into such a shape, defects in any pixelcan be easily corrected without adversely affecting other pixels.

Embodiment Mode 15

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 41 shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 41 is a top plan view showing theconnection relation between a pixel electrode and a power supply line.An equivalent circuit of the top plan view shown in FIG. 41 correspondsto FIG. 15, and has a structure where the transistors 1506 and 1507 thatare connected in series and the transistor 1508 are connected to oneelectrode of a light emitting element between a pixel electrode and apower supply line.

One electrode 1561 of the light emitting element is connected to anactive layer 1565 (one of the source and the drain) of the transistor1506 and an active layer 1566 (one of the source and the drain) of thetransistor 1508 through a wire 1562. The other of the source and thedrain of the transistor 1506 is connected to an active layer 1570 (oneof the source and the drain) of the transistor 1507 through the wire1571. The other of the source and the drain of the transistor 1507 isconnected to a wire 1572, and the other of the source and the drain ofthe transistor 1508 is connected to a wire 1568.

In this embodiment mode, at least one of the widths Y143, Y144, Y147,Y149, Y150, and Y151, and at least one of the widths Y145, Y146 and Y148are reduced. In that case, at least one of the widths Y143, Y144, Y147,Y149, Y150, and Y151, and at least one of the widths Y145, Y146 and Y148are preferably 3 μm or less.

Instead of reducing at least one of the widths Y143, Y144, Y147, Y149,Y150, and Y151, and at least one of the widths Y145, Y146 and Y148, atleast one of the widths Y141 and Y142 may be reduced. The latterstructure is preferably adopted instead of the former structure, sincedefective pixels can be corrected by cutting off only one portion of awire and the like. In that case, each of the widths Y141 and Y142 ispreferably 3 μm or less.

In the display device having the one electrode 1561 of the lightemitting element 101, the wire 1562, the active layer 1565, the activelayer 1566, the wire 1567, the wire 1568, the active layer 1570, and thewire 1571 that are formed into such a shape, defects in any pixel can beeasily corrected without adversely affecting other pixels.

Embodiment Mode 16

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 42A shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 42A is a top plan view showing theconnection relation between a pixel electrode (one of a pair ofelectrodes of a light emitting element) and a power supply line, andFIG. 42B is a cross sectional view along a line A-A′ of FIG. 42A. Anequivalent circuit of the top plan view shown in FIG. 42A corresponds toFIG. 12, and has a structure where at least two transistors that areconnected in series are provided between the pixel electrode (one of apair of electrodes of the light emitting element) and the power supplyline similarly to FIG. 36A and FIG. 37A.

A pixel electrode 4201 is connected to one of the source and the drainof the transistor 1204 having an active layer 4204 through a wire 4202.The other of the source and the drain of the transistor 1204 isconnected to one of the source and the drain of the transistor 1205having an active layer 4206 through a wire 4205. The other of the sourceand the drain of the transistor 1205 is connected to a wire 4207. InFIG. 42B, reference numeral 4208 denotes a semiconductor film containingan element belonging to group 13 (or 15) of the periodic table, which isnot shown in FIG. 42A since it is provided under the wire 4202, the wire4205 and the wire 4207. Note that a substrate is provided under a gatewire 4203, which is not shown in FIGS. 42A and 42B.

In this embodiment mode, the width Y161 of the wire 4202 in a portionwhere the wire 4202 does not overlap the pixel electrode 4201 and theactive layer 4204 when seen from the top surface is reduced. The widthY161 is preferably 3 μm or less.

Instead of reducing the width Y161, the width Y162 of the wire 4205 in aportion where the wire 4205 does not overlap the active layer 4204 andthe active layer 4206 may be reduced. The width Y162 is preferably 3 μmor less. Instead of reducing the width Y161 or Y162, the width Y163 ofthe wire 4207 in a portion where the wire 4207 does not overlap theactive layer 4206 may be reduced. The width Y163 is preferably 3 μm orless. All of the widths Y161, Y162 and Y163 may be reduced, or at leastone of them may be reduced.

In the display device having the wire 4202, the wire 4205, and the wire4207 that are formed into such a shape, defects in any pixel can beeasily corrected without adversely affecting other pixels.

Embodiment Mode 17

Described in this embodiment mode is another structure of a pixelportion of a display device where defective pixels can be easilycorrected.

FIG. 43A shows a layout corresponding to a part of one pixel in a pixelportion of a display device. FIG. 43A is a top plan view showing theconnection relation between a pixel electrode (one of a pair ofelectrodes of a light emitting element) and a power supply line, andFIG. 43B is a cross sectional view along a line A-A′ of FIG. 43A. Anequivalent circuit of the top plan view shown in FIG. 43A corresponds toFIG. 12, and has a structure where at least two transistors that areconnected in series are provided between the pixel electrode (one of apair of electrodes of the light emitting element) and the power supplyline similarly to FIG. 42A.

In FIG. 42A described in Embodiment Mode 16, a part of the active layer(corresponding to a channel forming region) in a portion where theactive layer does not overlap the semiconductor film 4208 containing anelement belonging to group 13 (or 15) of the periodic table is etched,and the pixel electrode 4201 is provided so as to overlap the wire 4202.FIG. 43A has almost the same structure as FIG. 42A, except in that aprotective film 4209 is provided so as to cover the active layer in aportion where the active layer does not overlap the channel formingregion, and the wire 4202 is provided so as to overlap the pixelelectrode 4201. That is to say, in this embodiment mode, at least one ofthe width Y161 of the wire 4202, the width Y162 of the wire 4205, andthe width Y163 of the wire 4207 may be reduced when seen from the topsurface. Each of the widths Y161, Y162 and Y163 is preferably 3 μm orless. Note that all of the widths Y161, Y162 and Y163 may be reduced.

In the display device having the wire 4202, the wire 4205, and the wire4207 that are formed into such a shape, defects in any pixel can beeasily corrected without adversely affecting other pixels.

Embodiment 1

Described in this embodiment is a structure of a display device wheredefective pixels can be easily corrected. Since a structure example of apixel is described in Embodiment Mode 2 with reference to FIG. 1,another structure example that is different from FIG. 1 is described inthis embodiment.

FIG. 21 shows an example of an equivalent circuit diagram correspondingto one pixel in a pixel portion of a display device. Each pixel has afirst transistor 2105, a second transistor 2106, a third transistor2107, a capacitor 2108, a light emitting element 2109, and one electrode2110 of the light emitting element 2109. The one electrode 2110 of thelight emitting element 2109 may be an anode or a cathode.

A gate electrode of the first transistor 2105 is connected to a gatesignal line 2104 (scan line), and one of a source and a drain thereof isconnected to a first source signal line 2102 (data line) while the otheris connected to a gate electrode of the third transistor 2107 and oneelectrode of the capacitor 2108. A gate electrode of the secondtransistor 2106 is connected to a second source signal line 2101, andone of a source and a drain thereof is connected to the other electrodeof the light emitting element 2109 while the other is connected to oneof a source and a drain of the third transistor 2107. The other of thesource and the drain of the third transistor 2107 is connected to apower supply line 2103. The other electrode of the capacitor 2108 isconnected to the power supply line 2103.

The capacitor 2108 has a function of holding a gate potential of thethird transistor 2107. Therefore, the capacitor 2108 is provided betweena gate electrode of the third transistor 2107 and the power supply line2103 in FIG. 21, though the invention is not limited to this structure.In other words, the capacitor 2108 is only required to be provided tohold the gate potential of the third transistor 2107. If the gatepotential of the third transistor 2107 can be held using the gatecapacitance of the third transistor 2107 or the like, the capacitor 2108is not necessarily provided.

As described in Embodiment Mode 2, the first to third transistors 2105to 2107 are not limited to the structure shown in FIG. 21. That is tosay, each of the first to third transistors 2105 to 2107 may be anN-channel transistor or a P-channel transistor. The active layer of eachtransistor may be formed of an amorphous semiconductor or a crystallinesemiconductor, and may have an LDD structure of a GOLD structure. Eachtransistor may have a forward staggered structure or an inverselystaggered structure, and a top gate structure or a bottom gatestructure. The gate electrode of each transistor may be formed both overand under the channel forming region, or either over or under thechannel forming region.

In order to implement the invention in FIG. 21, at least a part of thecurrent path between the power supply line 2103 and the other electrodeof the light emitting element 2109 (electrode connected to one of thesource and the drain of the second transistor 2106) may be interrupted.The current path between the other electrode of the light emittingelement 2109 and the power supply line 2103 is similar to theaforementioned structure of FIG. 12, and thus description thereof isomitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 22 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 2205, a second transistor 2206, a thirdtransistor 2207, a capacitor 2208, a light emitting element 2209, andone electrode 2210 of the light emitting element 2209. The one electrode2210 of the light emitting element 2209 may be an anode or a cathode.

A gate electrode of the first transistor 2205 is connected to a firstgate signal line 2204, and one of a source and a drain thereof isconnected to a first source signal line 2201 (data line) while the otheris connected to a gate electrode of the second transistor 2206, one of asource and a drain of the third transistor 2207, and one electrode ofthe capacitor 2208. One of a source and a drain of the second transistor2206 is connected to the other electrode of the light emitting element2209, while the other is connected to a power supply line 2202. A gateelectrode of the third transistor 2207 is connected to a second gatesignal line 2203, and the other of the source and the drain thereof isconnected to a power supply line 2202. The other electrode of thecapacitor 2208 is connected to the power supply line 2202.

In order to implement the invention in FIG. 22, at least a part of thecurrent path between the power supply line 2202 and the other electrodeof the light emitting element 2209 (electrode connected to one of thesource and the drain of the second transistor 2206) may be interrupted.The current path between the other electrode of the light emittingelement 2209 and the power supply line 2202 is similar to theaforementioned structure of FIG. 11, and thus description thereof isomitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 23 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first switch 2303, a second switch 2304, a transistor 2305,a capacitor 2306, a third switch 2307, a fourth switch 2308, a fifthswitch 2309, a light emitting element 2310, and one electrode 2311 ofthe light emitting element 2310. The one electrode 2311 of the lightemitting element 2310 may be an anode or a cathode.

A gate electrode of the transistor 2305 is connected to one electrode ofthe capacitor 2306, one terminal of the fourth switch 2308, and oneterminal of the fifth switch 2309. One of a source and a drain of thetransistor 2305 is connected to one terminal of the first switch 2303and one terminal of the second switch 2304, while the other is connectedto one terminal of the third switch 2307 and the other terminal of thefourth switch 2308. The other terminal of the first switch 2303 isconnected to a source signal line 2301, and the other terminal of thesecond switch 2304 is connected to a power supply line 2302. The otherelectrode of the capacitor 2306 is connected to the power supply line2302. The other terminal of the third switch 2307 is connected to theother electrode of the light emitting element 2310.

In order to implement the invention in FIG. 23, at least a part of thecurrent path between the power supply line 2302 and the other electrodeof the light emitting element 2310 (electrode connected to the otherterminal of the third switch 2307) may be interrupted.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 24 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 2405, a second transistor 2406, a switch2407, a capacitor 2408, a third transistor 2409, a fourth transistor2410, a light emitting element 2411, and one electrode 2412 of the lightemitting element 2411. The one electrode 2412 of the light emittingelement 2411 may be an anode or a cathode.

A gate electrode of the first transistor 2405 is connected to a firstgate signal line 2403, and one of a source and a drain thereof isconnected to the other electrode of the light emitting element 2411while the other is connected to one of a source and a drain of thesecond transistor 2406. A gate electrode of the second transistor 2406is connected to one terminal of the switch 2407, one electrode of thecapacitor 2408, and one of a source and a drain of the third transistor2409. The other of the source and the drain of the second transistor2406 is connected to a power supply line 2402. The other electrode ofthe capacitor 2408 is connected to the power supply line 2402. The otherof the source and the drain of the third transistor 2409 is connected toone of a source and a drain of the fourth transistor 2410. A gateelectrode of the fourth transistor 2410 is connected to a second gatesignal line 2404, and the other of the source and the drain thereof isconnected to a source signal line 2401.

In order to implement the invention in FIG. 24, at least a part of thecurrent path between the power supply line 2402 and the other electrodeof the light emitting element 2411 may be interrupted. The current pathbetween the other electrode of the light emitting element 2411 and thepower supply line 2402 is similar to the aforementioned structure ofFIG. 12, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 25 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. FIG.25 has almost the same structure as FIG. 24, except in that a fifthtransistor 2413 is provided instead of the switch 2407 that is providedin FIG. 24.

A gate electrode of the fifth transistor 2413 is connected to one of asource and a drain thereof and one of the source and the drain of thefourth transistor 2410. The other of the source and the drain of thefifth transistor 2413 is connected to one of the source and the drain ofthe third transistor 2409.

In order to implement the invention in FIG. 25, at least a part of thecurrent path between the power supply line 2402 and the other electrodeof the light emitting element 2411 may be interrupted. The current pathbetween the other electrode of the light emitting element 2411 and thepower supply line 2402 is similar to the aforementioned structure ofFIG. 12, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 26 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 2606, a first capacitor 2607, a secondcapacitor 2608, a second transistor 2606, a third transistor 2610, afourth transistor 2611, a fifth transistor 2612, a light emittingelement 2613, and one electrode 2614 of the light emitting element 2613.The one electrode 2614 of the light emitting element 2613 may be ananode or a cathode.

A gate electrode of the first transistor 2606 is connected to a secondgate signal line 2604, and one of a source and a drain thereof isconnected to a source signal line 2601 while the other is connected toone electrode of the first capacitor 2607, one electrode of the secondcapacitor 2608, and one of a source and a drain of the second transistor2609. The other electrode of the first capacitor 2607 is connected to apower supply line 2602. The other electrode of the second capacitor 2608is connected to one of a source and a drain of the third transistor 2610and a gate electrode of the fourth transistor 2611. A gate electrode ofthe second transistor 2609 is connected to a first gate signal line 2603and a gate electrode of the third transistor 2610. The other of thesource and the drain of the second transistor 2609 is connected to thepower supply line 2602 and one of a source and a drain of the fourthtransistor 2611. The other of the source and the drain of the thirdtransistor 2610 is connected to the power supply line 2602, the other ofthe source and the drain of the fourth transistor 2611, and one of asource and a drain of the fifth transistor 2612. A gate electrode of thefifth transistor 2612 is connected to a third gate signal line 2605, andthe other of the source and the drain thereof is connected to the otherelectrode of the light emitting element 2613.

In order to implement the invention in FIG. 26, at least a part of thecurrent path between the power supply line 2602 and the other electrodeof the light emitting element 2613 may be interrupted. The current pathbetween the other electrode of the light emitting element 2613 and thepower supply line 2602 is similar to the aforementioned structure ofFIG. 12, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 27A shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 2706, a first capacitor 2707, a secondtransistor 2708, a third transistor 2709, a fourth transistor 2710, alight emitting element 2711, and one electrode 2712 of the lightemitting element 2711. The one electrode 2712 of the light emittingelement 2711 may be an anode or a cathode.

A gate electrode of the first transistor 2706 is connected to a secondgate signal line 2704, and one of a source and a drain thereof isconnected to a source signal line 2701 while the other is connected toone electrode of the first capacitor 2707 and a gate electrode of thethird transistor 2709. The other electrode of the first capacitor 2707is connected to a power supply line 2702. A gate electrode of the secondtransistor 2708 is connected to a first gate signal line 2703, and oneof a source and a drain thereof is connected to the source signal line2701 while the other is connected to one of a source and a drain of thethird transistor 2709 and one of a source and a drain of the fourthtransistor 2710. The other of the source and the drain of the thirdtransistor 2709 is connected to the power supply line 2702. A gateelectrode of the fourth transistor 2710 is connected to a third gatesignal line 2705, and the other of the source and the drain thereof isconnected to the other electrode of the light emitting element 2711.

Description is made on FIG. 27B. In FIG. 27A, one of the source and thedrain of the first transistor 2706 is connected to the source signalline 2701. FIG. 27B has almost the same structure as FIG. 27A, except inthat one of the source and the drain of the first transistor 2706 isconnected to the other of the source and the drain of the secondtransistor 2708, one of the source and the drain of the third transistor2709, and one of the source and the drain of the fourth transistor 2710.

In order to implement the invention in FIGS. 27A and 27B, at least apart of the current path between the power supply line 2702 and theother electrode of the light emitting element 2711 may be interrupted.The current path between the other electrode of the light emittingelement 2711 and the power supply line 2702 is similar to theaforementioned structure of FIG. 12, and thus description thereof isomitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 28 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 2806, a first capacitor 2807, a secondcapacitor 2808, a second transistor 2809, a third transistor 2810, afourth transistor 2811, a light emitting element 2812, and one electrode2813 of the light emitting element 2812. The one electrode 2813 of thelight emitting element 2812 may be an anode or a cathode.

A gate electrode of the first transistor 2806 is connected to a firstgate signal line 2803, and one of a source and a drain thereof isconnected to a source signal line 2801 while the other is connected toone electrode of the first capacitor 2807. The other electrode of thefirst capacitor 2807 is connected to one electrode of the secondcapacitor 2808, one of a source and a drain of the second transistor2809, and a gate electrode of the third transistor 2810. The otherelectrode of the second capacitor 2808 is connected to a power supplyline 2802. A gate electrode of the second transistor 2809 is connectedto a second gate signal line 2804, and the other of the source and thedrain thereof is connected to one of a source and a drain of the thirdtransistor 2810 and one of a source and a drain of the fourth transistor2811. The other of the source and the drain of the third transistor 2810is connected to the power supply line 2802. A gate electrode of thefourth transistor 2811 is connected to a third gate signal line 2805,and the other of the source and the drain is connected to the otherelectrode of the light emitting element 2812.

In order to implement the invention in FIG. 28, at least a part of thecurrent path between the power supply line 2802 and the other electrodeof the light emitting element 2812 may be interrupted. The current pathbetween the other electrode of the light emitting element 2812 and thepower supply line 2802 is similar to the aforementioned structure ofFIG. 12, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 29 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first switch 2903, a first transistor 2904, a second switch2905, a capacitor 2906, a second transistor 2907, a light emittingelement 2908, and one electrode 2909 of the light emitting element 2908.The one electrode 2909 of the light emitting element 2908 may be ananode or a cathode.

One terminal of the first switch 2903 is connected to a source signalline 2901, while the other terminal thereof is connected to one of asource and a drain of the first transistor 2904, a gate electrode of thefirst transistor 2904, and one terminal of the second switch 2905. Theother of the source and the drain of the first transistor 2904 isconnected to a power supply line 2902. The other terminal of the secondswitch 2905 is connected to one electrode of the capacitor 2906 and agate electrode of the second transistor 2907. The other electrode of thecapacitor 2906 is connected to the power supply line 2902. One of asource and a drain of the second transistor 2907 is connected to thepower supply line 2902, while the other is connected to the otherelectrode of the light emitting element 2908.

In order to implement the invention in FIG. 29, at least a part of thecurrent path between the power supply line 2902 and the other electrodeof the light emitting element 2908 may be interrupted. The current pathbetween the other electrode of the light emitting element 2908 and thepower supply line 2902 is similar to the aforementioned structure ofFIG. 11, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 30 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first switch 3003, a first transistor 3004, a second switch3005, a capacitor 3006, a second transistor 3007, a light emittingelement 3008, and one electrode 3009 of the light emitting element 3008.The one electrode 3009 of the light emitting element 3008 may be ananode or a cathode.

One terminal of the first switch 3003 is connected to a source signalline 3001, while the other terminal is connected to one of a source anda drain of the first transistor 3004 and one terminal of the secondswitch 3005. A gate electrode of the first transistor 3004 is connectedto the other terminal of the second switch 3005, one electrode of thecapacitor 3006, and a gate electrode of the second transistor 3007. Theother of the source and the drain of the first transistor 3004 isconnected to a power supply line 3002. The other electrode of thecapacitor 3006 is connected to the power supply line 3002. One of asource and a drain of the second transistor 3007 is connected to thepower supply line 3002, while the other is connected to the otherelectrode of the light emitting element 3008.

In order to implement the invention in FIG. 30, at least a part of thecurrent path between the power supply line 3002 and the other electrodeof the light emitting element 3008 may be interrupted. The current pathbetween the other electrode of the light emitting element 3008 and thepower supply line 3002 is similar to the aforementioned structure ofFIG. 11, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 31 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 3108, a first capacitor 3109, a secondcapacitor 3110, a second transistor 3111, a third transistor 3112, afourth transistor 3113, a fifth transistor 3114, a light emittingelement 3115, and one electrode 3116 of the light emitting element 3115.The one electrode 3116 of the light emitting element 3115 may be ananode or a cathode.

A gate electrode of the first transistor 3108 is connected to a firstgate signal line 3103, and one of a source and a drain thereof isconnected to a source signal line 3101 while the other is connected toone electrode of the first capacitor 3109, one electrode of the secondcapacitor 3110, and one of a source and a drain of the second transistor3111. The other electrode of the first capacitor 3109 is connected to apower supply line 3102. The other electrode of the second capacitor 3110is connected to one of a source and a drain of the third transistor 3112and a gate electrode of the fourth transistor 3113. A gate electrode ofthe second transistor 3111 is connected to a second gate signal line3104, and the other of the source and the drain thereof is connected toone of a source and a drain of the fourth transistor 3113 and one of asource and a drain of the fifth transistor 3114. A gate electrode of thethird transistor 3112 is connected to a third gate signal line 3105, andthe other of the source and the drain thereof is connected to a wire3107 for initialization. The other of the source and the drain of thefourth transistor 3113 is connected to the other electrode of the lightemitting element 3115. A gate electrode of the fifth transistor 3114 isconnected to a fourth gate signal line 3106, and the other of the sourceand the drain thereof is connected to the power supply line 3102.

In order to implement the invention in FIG. 31, at least a part of thecurrent path between the power supply line 3102 and the other electrodeof the light emitting element 3115 may be interrupted. The current pathbetween the other electrode of the light emitting element 3115 and thepower supply line 3102 is similar to the aforementioned structure ofFIG. 12, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 32 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first capacitor 3203, a transistor 3204, a first switch3205, a second switch 3206, a light emitting element 3207, and oneelectrode 3208 of the light emitting element 3207. The one electrode3208 of the light emitting element 3207 may be an anode or a cathode.

One electrode of the first capacitor 3203 is connected to a sourcesignal line 3201, while the other electrode is connected to a gateelectrode of the transistor 3204 and one terminal of the first switch3205. One of a source and a drain of the transistor 3204 is connected toa power supply line 3202, while the other is connected to the otherterminal of the first switch 3205 and one terminal of the second switch3206. The other terminal of the second switch 3206 is connected to theother electrode of the light emitting element 3207.

In order to implement the invention in FIG. 32, at least a part of thecurrent path between the power supply line 3202 and the other electrodeof the light emitting element 3207 may be interrupted.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 33 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first capacitor 3303, a first transistor 3304, a secondtransistor 3305, a first switch 3306, a second switch 3307, a lightemitting element 3308, and one electrode 3309 of the light emittingelement 3308. The one electrode 3309 of the light emitting element 3308may be an anode or a cathode.

One electrode of the first capacitor 3303 is connected to a sourcesignal line 3301, while the other electrode is connected to a gateelectrode of the first transistor 3304, a gate electrode of the secondtransistor 3305, and one terminal of the second switch 3307. One of asource and a drain of the first transistor 3304 is connected to oneterminal of the first switch 3306, while the other is connected to oneof a source and a drain of the second transistor 3305, the otherterminal of the second switch 3307, and the other electrode of the lightemitting element 3308. The other of the source and the drain of thesecond transistor 3305 is connected to a low potential power supply.Thus, the first transistor 3304 and the second transistor 3305constitute a CMOS inverter circuit. The other terminal of the firstswitch 3306 is connected to a power supply line 3302.

In order to implement the invention in FIG. 33, at least a part of thecurrent path between the power supply line 3302 and the other electrodeof the light emitting element 3308 may be interrupted.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

FIG. 34 shows another example of an equivalent circuit diagramcorresponding to one pixel in a pixel portion of a display device. Eachpixel has a first transistor 3404, a capacitor 3405, a second transistor3406, a third transistor 3407, a light emitting element 3408, and oneelectrode 3409 of the light emitting element 3408. The one electrode3409 of the light emitting element 3408 may be an anode or a cathode.

A gate electrode of the first transistor 3404 is connected to a gatesignal line 3403, and one of a source and a drain thereof is connectedto a source signal line 3401 while the other is connected to oneelectrode of the capacitor 3405, one of a source and a drain of thesecond transistor 3406, and the other electrode of the light emittingelement 3408. The other electrode of the capacitor 3405 is connected toa gate electrode of the second transistor 3406 and one of a source and adrain of the third transistor 3407. The other of the source and thedrain of the second transistor 3406 is connected to a power supply line3402. A gate electrode of the third transistor 3407 is connected to agate signal line 3403, and the other of the source and the drain thereofis connected to the power supply line 3402.

In order to implement the invention in FIG. 34, at least a part of thecurrent path between the power supply line 3402 and the other electrodeof the light emitting element 3408 may be interrupted. The current pathbetween the other electrode of the light emitting element 3408 and thepower supply line 3402 is similar to the aforementioned structure ofFIG. 11, and thus description thereof is omitted here.

The invention adopts a structure where the width of a wire correspondingto a portion to be cut off is reduced to correct a defective pixeleasily. As specific examples of the structure where the width of a wirecorresponding to a portion to be cut off is reduced, the structuresdescribed in Embodiment Modes 6 to 9 may be employed, and thusdescription thereof is omitted here.

The drawings shown in this embodiment are just examples. That is to say,the invention is not limited to the conductivity of transistors and thestructures shown in the drawings, and either an N-channel transistor ora P-channel transistor may be adopted.

Embodiment 2

The display device of the invention can be applied to a display area ofvarious electronic apparatuses. In particular, the display device of theinvention is desirably used for mobile devices that are required to bereduced in thickness and weight.

The display device shown in the aforementioned embodiment modes andembodiment may be incorporated in a housing of electronic apparatusessuch as a television set (also simply referred to as a TV, a television,or a television receiver), a camera (such as a video camera and adigital camera), a goggle type display, a navigation system, an audioreproducing device (such as a car audio system and an audio componentsystem), a computer, a game machine, a portable information terminal(such as a mobile computer, a mobile phone set, a portable game machineand an electronic book), an image reproducing device provided with arecording medium (specifically, a device that reproduces a recordingmedium such as a DVD (Digital Versatile Disc), a HD DVD (High DefinitionDVD), and a Blu-ray disc, and that has a display for displaying thereproduced image), and other electronic devices each having a displayarea. Specific examples of the electronic apparatuses are shown in FIGS.8A to 8F and FIG. 10.

A portable information terminal shown in FIG. 8A includes a main body9201, a display area 9202 and the like. The display devices shown inEmbodiment Modes 1 to 9 may be applied to the display area 9202. Thedisplay device that is one mode of the invention allows a portableinformation terminal with high display quality, where no bright spotsare included (even though point defects are included) and degradation inimage quality of the entire screen is reduced, to be provided with highyield and at low cost.

A digital video camera shown in FIG. 8B includes a display area 9701, adisplay area 9702 and the like. The display device shown in EmbodimentModes 1 to 9 may be applied to the display area 9701. The display devicethat is one mode of the invention allows a digital video camera withhigh display quality, where no bright spots are included (even thoughpoint defects are included) and degradation in image quality of theentire screen is reduced, to be provided with high yield and at lowcost.

A portable terminal shown in FIG. 8C includes a main body 9101, adisplay area 9102 and the like. The display devices shown in EmbodimentModes 1 to 9 may be applied to the display area 9102. The display devicethat is one mode of the invention allows a portable terminal with highdisplay quality, where no bright spots are included (even though pointdefects are included) and degradation in image quality of the entirescreen is reduced, to be provided with high yield and at low cost.

A portable television set shown in FIG. 8D includes a main body 9301, adisplay area 9302 and the like. The display devices shown in EmbodimentModes 1 to 9 may be applied to the display area 9302. The display devicethat is one mode of the invention allows a portable television set withhigh display quality, where no bright spots are included (even thoughpoint defects are included) and degradation in image quality of theentire screen is reduced, to be provided with high yield and at lowcost. The display device of the invention can be widely applied to asmall size television set incorporated in a portable terminal such as amobile phone, a medium size one that is portable, and a large size one(e.g., 40 inches in size or more).

A portable computer shown in FIG. 8E includes a main body 9401, adisplay area 9402 and the like. The display devices shown in EmbodimentModes 1 to 9 may be applied to the display area 9402. The display devicethat is one mode of the invention allows a portable computer with highdisplay quality, where no bright spots are included (even though pointdefects are included) and degradation in image quality of the entirescreen is reduced, to be provided with high yield and at low cost.

A television set shown in FIG. 8F includes a main body 9501, a displayarea 9502 and the like. The display devices shown in Embodiment Modes 1to 9 may be applied to the display area 9502. The display device that isone mode of the invention allows a television set with high displayquality, where no bright spots are included (even though point defectsare included) and degradation in image quality of the entire screen isreduced, to be provided with high yield and at low cost.

FIG. 10 shows an example of an electronic book that incorporates adouble-sided display panel 4303. A first housing 4305 has a firstdisplay area 4301, and a second housing 4306 has an operating button4304 and a second display area 4307. The double-sided display panel 4303has a first display surface, and a second display surface 4302 that isthe opposite surface of the first display surface. The double-sideddisplay panel 4303 is interposed between the first housing 4305 and thesecond housing 4306. The display devices shown in Embodiment Modes 1 to9 may be applied to each display area.

As an example of usage of the electronic book where the double-sideddisplay panel 4303 is interposed, it is convenient to read text on thefirst display area 4301 and the second display surface 4302, and to seea drawing on the second display area 4307 and the first display surface.Since the double-sided display panel 4303 cannot display the firstdisplay surface and the second display surface 4302 at the same time,display of the first display surface is switched to the display of thesecond display surface when moving the first display surface and thesecond display surface 4302.

Further, after the first display area 4301 and the first display surfaceare read, the second display surface and the second display area 4307display the next page when the next page, namely the double-sideddisplay panel is turned at a certain angle. In addition, after thesecond display surface 4302 and the second display area 4307 are read,the first display surface and the first display area 4301 display thenext page when the double-sided display panel is turned at a certainangle. Thus, the switching of display surfaces is made invisible, andvisual incongruity can be reduced. In order to further reduce theincongruity, a dual emission panel is desirably provided over a flexiblesubstrate. The display device that is one mode of the invention allowsan electronic book with high display quality, where no bright spots areincluded (even though point defects are included) and degradation inimage quality of the entire screen is reduced, to be provided with highyield and at low cost.

If the aforementioned electronic apparatuses use a rechargeable battery,the life of them increases with reduction in the power consumption ofthe display device, thereby the time for charging the rechargeablebattery can be reduced.

In addition to the aforementioned electronic apparatuses, the inventionmay be applied to a front type or a rear type projector.

As set forth above, the application range of the invention is so widethat the invention can be applied to electronic apparatuses of allfields.

This application is based on Japanese Patent Application serial No.2005-024631 filed in Japan Patent Office on Jan. 31, 2005, the entirecontents of which are hereby incorporated by reference.

1. (canceled)
 2. A display device comprising a pixel, the pixelcomprising: a light-emitting element over a substrate; a firsttransistor over the substrate; and a first wiring electrically connectedto one of a source and a drain of the first transistor, wherein thefirst wiring is a power supply line and configured to supply current tothe light-emitting element, wherein the first wiring comprises a firstregion overlapping with a contact hole and a second region having awidth narrower than a width of the first region, and wherein the firstregion of the first wiring does not overlap with a pixel electrode ofthe light-emitting element.
 3. A display device comprising a pixel, thepixel comprising: a light-emitting element over a substrate; a firsttransistor, a second transistor, a third transistor, a fourthtransistor, a fifth transistor, and a sixth transistor over thesubstrate; a first wiring electrically connected to one of a source anda drain of the first transistor; and a second wiring electricallyconnected to one of a source and a drain of the second transistor,wherein the other of the source and the drain of the first transistor iselectrically connected to the other of the source and the drain of thesecond transistor and one of a source and a drain of the thirdtransistor, wherein the other of the source and the drain of the thirdtransistor is electrically connected to one of a source and a drain ofthe fourth transistor and one of a source and a drain of the fifthtransistor, wherein the other of the source and the drain of the fourthtransistor is electrically connected to the light-emitting element,wherein the other of the source and the drain of the fifth transistor iselectrically connected to one of a source and a drain of the sixthtransistor, wherein the first wiring is a power supply line andconfigured to supply current to the light-emitting element, wherein thefirst wiring comprises a first region overlapping with a contact holeand a second region having a width narrower than a width of the firstregion, and wherein the first region of the first wiring does notoverlap with a pixel electrode of the light-emitting element.